Packet communication systems

ABSTRACT

The present invention provides a packet communication system has a mobile host, a home agent, a correspondent host, and a mobility agent, wherein the mobility agent operates in such a way that in the case of an active mode and no need for buffering of packet, the mobility agent forwards a packet received from the home agent or the correspondent host, to the mobile host, that in the case of the active mode and necessity for buffering of packet, the mobility agent buffers the packet, and that in the case of an idle mode, the mobility agent buffers the packet and notifies the mobile host of arrival of the packet, in order to prevent the loss of a packet addressed to a mobile host, to decrease the traffic of Binding Update packets, to decrease the transmission frequency of Binding Update packets where the mobile host sends or receives no packet for a long period of time, and to send a packet a destination of which is a node present at a mobile network.

TECHNICAL FIELD OF THE INVENTION

[0001] The present invention relates to packet communication systemscapable of transmitting packets to mobile nodes.

RELATED BACKGROUND ARTS

[0002] A configuration of a conventional packet communication systemwill be described. The configuration of the packet communication systemis shown in FIG. 1. As shown in FIG. 1, the conventional packet systemcomprises a router R, a home agent HR, an access router AR, a MobileHost MH , and a Correspondent Host CH and they are connected among them.

[0003] The packet communication system is comprised of nodes and links.The nodes are devices for sending and receiving packets according toTCP/IP. The links are communication paths for transmitting packets froma node to another node by wire transmission or wireless transmission.How to determine the numbers of links and nodes and the connectionlayout thereof is optional, and requirements are only that each node isdirectly or indirectly connected to all the other nodes by at least onelink. This connection layout is called a network, which is depicted as acloudlike illustration in FIG. 1. The links and nodes are identified bytheir respective addresses (addresses defined by IPv6) An address iscomprised of a Subnet-prefix and a node identifier, wherein theSubnet-prefix identifies a link to which a node is connected and whereinthe node identifier identifies a node connected to a link.

[0004] Each node is classified under a router, an access router, a homeagent, a mobile host, and a correspondent host. The router is a node forforwarding a packet whose destination address is different from its ownaddress, to another appropriate node. The access router is a router forproviding a link to which the mobile host can obtain access. The homeagent is a router that can forward a packet directed to the mobile host,to a link at which the mobile host is located. The routers, accessrouters, and home agent regularly exchange information indicatingconnection relations of links with the routers, access routers, and homeagent necessary for routing processing, by a routing protocol such asOSPF (Open Shortest Path First) or BGP (Border Gateway Protocol). Themobile host is a node that implements communications with thecorrespondent host while moving from link to link. The correspondenthost is a node that implements communications with the mobile host.

[0005] Each link is classified under a home link and a foreign link. Thehome link is a link to which the mobile host belongs, and the foreignlink is a link except for the home link. When there exist a plurality ofmobile hosts, the home and foreign links are defined for every mobilehost. The mobile host is assigned a home address by the home link and ac/o (care of) address by the foreign link. The home address is anaddress used when the mobile host is present at the home link and at theforeign links. The c/o address is an address used when the mobile hostis present at the foreign links. This c/o address is a forwardingdestination address of a packet directed to the home address.

[0006] The operation of the conventional packet communication systemwill be described. After the mobile host has moved from its home link toa foreign link, it acquires a c/o address used at the foreign link andthen sends a packet including a Binding Update option, to the homeagent. In the description hereinafter, this packet will be called simplya Binding Update packet. The Binding Update packet includes the homeaddress and the c/o address of the mobile host, and a correspondencebetween the home address and the c/o address will be called binding.When receiving the Binding Update packet from the mobile host, the homeagent stores the binding and sends a packet including a BindingAcknowledgement option as an acknowledgement response to the mobilehost. In the description hereinafter, this packet will be called simplya Binding Acknowledgement packet. When receiving the BindingAcknowledgement packet from the home agent, the mobile host recognizesthe storage of the binding at the home agent.

[0007] When the correspondent host sends a packet directed to the homeaddress of the mobile host, the packet is routed from the correspondenthost to the home link by the routers in the network. When thedestination of the packet is the home address of the binding, the homeagent receives the packet instead of the mobile host, generates a packeta destination of which is the c/o address of the binding, puts thereceived packet in a payload of the generated packet, and forwards thepacket. The method of putting a certain packet into a payload of anotherpacket and forwarding the packet is called tunneling and such a packetis called a tunneling packet. This tunneling packet is routed from thehome agent to the mobile host by the routers in the network. The mobilehost receives the tunneling packet and takes the packet out of thepayload of the tunneling packet, thus finally receiving the packet thedestination of which is its own home address.

[0008] The mobile host receiving the tunneling packet may send a BindingUpdate packet to the correspondent host. Receiving the Binding Updatepacket, the correspondent host stores the binding. When thecorrespondent host sends a packet whose destination is the home addressindicated by the stored binding, it sets the c/o address to thedestination of the packet and sends the packet provided with a routingheader option in which the home address of the binding is set. Whenreceiving the packet with the routing header option, the mobile hostreplaces the c/o address of the destination with the home address,thereby receiving the packet the destination of which is the homeaddress, at last.

[0009] After that, every time the mobile host moves to another foreignlink and acquires a new c/o address, it notifies the home agent and thecorrespondent host of new binding by a Binding Update packet. Throughthis operation of the mobile host, the packet sent from thecorrespondent host is forwarded via the home agent or directly from thecorrespondent host to the mobile host located at a foreign link.

[0010] The foregoing packet communication system of the prior art,however, has the problem that there occurs a packet loss where themobile host moves quickly between foreign links far off from the homelink or the correspondent host. When the mobile host moves to a foreignlink far off from the home link or the correspondent host, the number ofpassing nodes and links during transmission of a packet, i.e., thenumber of hops increases. Since the increase in the number of hopsbetween the home link or the correspondent host and the foreign linkresults in increasing a packet transmission delay, the time becomeslonger for the transmission of the Binding Update packet from the mobilehost to the home agent or the correspondent host.

[0011] The quick movement of the mobile host between foreign linksresults in shortening stay periods at the respective links, because themobile host stays at each foreign link for a shorter time. If a stayperiod is shorter than the transmission period, there will occur aphenomenon in which the mobile host has already moved to another foreignlink at the time of arrival of the Binding Update packet at the homeagent or the correspondent host. In this case, a packet addressed to themobile host is forwarded to the foreign link where the mobile hoststayed before, and the packet is lost without being received by themobile host. A conceivable example of such quick movement of the mobilehost between foreign links is a situation in which cells in a cellularmobile telecommunications system are foreign links.

[0012] In association with the foregoing problem, the packetcommunication system of the prior art further has the problem that whenthe mobile host moves between foreign links far off from the home linkor the correspondent host, the number of hops that one Binding Updatepacket passes becomes large, so as to consume a lot of resources oflinks.

[0013] The packet communication system of the prior art also has theproblem that, while there occurs no packet transmission between themobile host and the correspondent host for a long time, the mobile hostmust also send the Binding Update packet to the home agent at every timeof its movement between links because of characteristics of anapplication employed. This increases the load for processing of BindingUpdate packets and Binding Acknowledgement packets at the home agent andalso poses the problem of consuming the resources of links bytransmission of Binding Update packets and Binding Acknowledgementpackets.

[0014] The present invention has been accomplished under thecircumstances as described above, and an object of the present inventionis to provide mobility agent, mobile host, home agent and packetcommunication systems capable of preventing the loss of packetsaddressed to the mobile host, reducing the traffic volume of BindingUpdate packets, reducing the transmission frequency of Binding Updatepackets in the case where a long time has passed without transmission ofa packet at the mobile host, and transmitting a packet whose destinationis a node located in a mobile network, a method of controlling them anda computer program for executing the method.

DISCLOSURE OF THE INVENTION

[0015] The mobility agent used in the packet communication systemaccording to the present invention is a mobility agent for forwarding areceived packet to a mobile host on the basis of the destination addressincluded in the received packet, comprising memory means for storingdata includes in a signal sent from the mobile host, the datarepresenting the correspondence between the home address and theforwarding destination address, operation mode, and whether or notbuffering of a packet is necessary every the mobile host, and sending areception acknowledgement signal to the mobile host which sent thesignal, when the memory means has stored the data. In the arrangement,under the control of the transmission/reception of the received packetaccording to the status of the mobile host and the status of whether ornot buffering of packet is necessary, the resource of the packetcommunication system may be effectively utilized.

[0016] Further the mobile host used in the packet communication systemaccording to the present invention is a mobile host which performs thepacket communication between the mobile host and the correspondencehost, featured by forwarding of data representing the correspondencebetween home address of the mobile host and the forwarding destinationaddress, data representing the operation mode, either one of active modeor idle mode of itself, and data instructing necessity of buffering orno necessity with respect to the packet to be received to the mobilityagent and reception of a reception acknowledgement signal regarding thesent data. Thus, by sending the operation mode and a request for whetheror not buffering is necessary, the mobility agent receiving them canrealize the effective packet transmission/reception in the packetcommunication system. Further, by switching over the operation mode,when the mobility agent is in the idle status, the power consumption ofthe mobility agent decrease and it is possible to realize low powerconsumption in the mobile host.

[0017] Further, a mobile router used in the packet communicationaccording to the present invention is a mobile transmitting a packet ofwhich forwarding destination address is not the address, to anotherproper node in a mobile network or a stationary network or betweenmobile networks, characterized by sending data representing theoperation mode, either one of active mode or idle mode, and datainstructing whether or not buffering of a packet is necessary withrespect to a packet to be received to the mobility agent to the mobilityagent, and reception of a reception acknowledgement data with respect tothe sent data.

[0018] Further, the present invention realizes the effective realizationof the resource of the packet communication system by providing a methodof controlling these mobility agent, mobile host and the mobile router,and a computer program for executing process of the method.

[0019] Further, a packet communication system according to the presentinvention is a packet communication system comprising a home agent forproviding a home link for a mobile host, a plurality of access routersfor providing foreign links for the mobile host, and a mobility agentincluding a plurality of access routers in an area thereof, in which ahome address is used when the mobile host is present at the home linkand in which the home address and a c/o address are used when the mobilehost is present at a foreign link, wherein the mobile host comprises:first notifying means for notifying the mobility agent of acorrespondence between the home address and the c/o address, anoperating mode indicating either an active mode or an idle mode, andwhether or not buffering of a packet is necessary; and second notifyingmeans for notifying the home agent of a correspondence between the homeaddress and an address of the mobility agent, wherein the home agentcomprises first forwarding means for forwarding a packet directed to thehome address, received from a correspondent host, to the address of themobility agent notified of by the mobile host, wherein the correspondenthost comprises sending means for sending a packet directed to the homeaddress, to the address of the mobility agent notified of by the mobilehost, wherein the mobility agent comprises: second forwarding means forforwarding a packet received from the home agent or the correspondenthost, to the mobile host; and buffering means for buffering a packet;and third notifying means for notifying the mobile host of arrival of apacket, and wherein the mobility agent is configured so that in theactive mode and without necessity for buffering of a packet, themobility agent forwards a packet received from the home agent or thecorrespondent host, to the mobile host, so that in the active mode andwith necessity for buffering of a packet, the mobility agent buffers apacket, and so that in the idle mode the mobility agent buffers a packetand notifies the mobile host of arrival of the packet.

[0020] The system may also employ a configuration comprising a pluralityof mobility agents.

[0021] The system may also employ such a configuration that in theactive mode, where the mobile host moves between foreign links in thearea of the mobility agent, the mobile host notifies the mobility agentof the correspondence between the home address and the c/o address, theoperating mode indicating the active mode, and the necessity forbuffering of a packet, before moving between the foreign links, and themobile host notifies the mobility agent of a correspondence between thehome address and a c/o address used at the destination foreign link, theoperating mode indicating the active mode, and no necessity forbuffering of a packet, after having moved between the foreign links.

[0022] The system may also employ such a configuration that in the idlemode, where the mobile host moves between foreign links in the area ofthe mobility agent, the mobile host notifies neither of the mobilityagent, the home agent, and the correspondent host of anything.

[0023] The system may also employ such a configuration that in theactive mode, where the mobile host moves from a foreign link in an areaof a certain mobility agent to a foreign link in an area of anothermobility agent different therefrom, the mobile host notifies themobility agent of the correspondence between the home address and thec/o address, the operating mode indicating the active mode, and thenecessity for buffering of a packet, before moving between the foreignlinks, and the mobile host notifies the mobility agent of acorrespondence between the home address and a c/o address used at thedestination foreign link, the operating mode indicating the active mode,and no necessity for buffering of a packet and also notifies the homeagent and the correspondent host of a correspondence between the homeaddress and an address of the mobility agent, after having moved betweenthe foreign links.

[0024] The system may also employ such a configuration that in the idlemode, where the mobile host moves from a foreign link in an area of acertain mobility agent to a foreign link of another mobility agentdifferent therefrom, the mobile host notifies the mobility agent of acorrespondence between the home address and a c/o address used at thedestination foreign link, the operating mode indicating the idle mode,and the necessity for buffering of a packet and also notifies the homeagent and a correspondent host of the correspondence between the homeaddress and an address of the mobility agent, after having moved betweenthe foreign links.

[0025] The system may also employ such a configuration that the homeagent and access routers are base stations, the home link and foreignlinks are radio communication links, and the mobile host is a mobilestation.

[0026] Another packet communication system comprising a stationarynetwork and a mobile network, may also adopt a configuration wherein thestationary network comprises a home agent adapted to the mobile network,a mobility agent, a correspondent host, and an access router, whereinthe mobile network comprises at least one mobile router and a pluralityof access routers, and wherein the mobile network moves between foreignlinks provided by the stationary network or another mobile network.

[0027] Still another packet communication system comprising a stationarynetwork and a mobile network, may also adopt a configuration wherein thestationary network comprises a home agent adapted to the mobile network,a mobility agent, a correspondent host, and an access router, whereinthe mobile network comprises at least one mobile router and a pluralityof stationary hosts, and wherein the mobile network moves betweenforeign links provided by the stationary network or another mobilenetwork.

[0028] The system may also employ such a configuration that the mobilerouter comprises: first notifying means for notifying the mobility agentof a correspondence between a home address and a c/o address, anoperating mode indicating either an active mode or an idle mode, andwhether or not buffering of a packet is necessary; second notifyingmeans for notifying the home agent of a correspondence between the homeaddress and an address of the mobility agent; and Subnet-prefixnotifying means for notifying the mobility agent and the home agent of aSubnet-prefix for identifying a link included in the mobile network.

[0029] The system may also employ such a configuration that the mobilenetwork comprises at least one mobility agent.

[0030] The system may also employ such a configuration that, when anaccess router exists in an area where service areas of a plurality ofmobility agents overlap with each other, the access router is free toselect either one of the plurality of mobility agents.

[0031] When the packet communication system is constructed employingeither of the configurations as described above, the mobility agentworks to buffer packets so as to be able to prevent the loss of packetssent from the correspondent host to the mobile host even if the mobilehost frequently moves between foreign links. A conceivable case wherethe mobile host frequently moves between foreign links is a situation inwhich the access routers in the packet communication system are basestations in a mobile telecommunications system, the mobile host is amobile station, and the foreign links are radio links between the basestations and the mobile station. In this case, movement of the mobilestation between base stations, i.e., between radio links is calledhandover. When the present invention is applied to the mobiletelecommunications systems, it is feasible to prevent the loss ofpackets sent from the correspondent host to the mobile station.

[0032] Even if the mobile host frequently moves between foreign linksthe mobile host is required merely to send the Binding Update packet toonly the mobility agent, which can reduce the traffic of Binding Updatepackets appearing in the packet communication system, where the mobilityagent is located nearer to the mobile host than the home agent and thecorrespondent host are. This effect is also achieved in the foregoingmobile telecommunications systems.

[0033] The idle mode is used where the mobile host sends or receives nopacket for a long period of time, which can reduce the traffic ofBinding Update packets appearing in the packet communication system.Further, since it is feasible to reduce the transmission frequency ofBinding Update packets from the mobile host, the invention also presentsthe effect of reducing power consumption of the battery at the mobilehost. This effect is also achieved in the aforementioned mobiletelecommunications systems.

[0034] Further, the invention provides the effect of permitting thecorrespondent host to send a packet addressed to a stationary host or amobile host present in a mobile network. This effect is not enjoyed withonly packets addressed to nodes present in mobile networks connected tothe stationary network, but is also enjoyed similarly with packetsaddressed to stationary hosts and mobile hosts present in a mobilenetwork connected to another mobile network.

[0035] When the mobile network is provided with at least one mobilityagent, it can provide such operating modes as the buffering of packet,the active mode, and the idle mode for the mobile host or another mobilenetwork moving between foreign links provided by the mobile network.

[0036] When an access router is present in an area in which serviceareas of a plurality of mobility agents overlap with each other, it isfree to select either of the mobility agents, whereby in the event ofabnormal stop of one mobility agent because of some trouble or the like,the mobile host can continue communications by switching the mobilityagent to another mobility agent. It also becomes feasible to distributethe traffic to a plurality of mobile hosts present at foreign links ofone access router, among a plurality of mobility agents.

BRIEF DESCRIPTION OF THE DRAWINGS

[0037]FIG. 1 is a diagram showing a configuration of a conventionalpacket communication system.

[0038]FIG. 2 is a diagram showing a configuration example of a packetcommunication system according to the present invention.

[0039]FIG. 3 is a diagram showing a configuration of a Binding Updatepacket.

[0040]FIG. 4 is a diagram showing a configuration of a BindingAcknowledgement packet.

[0041]FIG. 5 is a diagram showing a configuration of a Paging Requestpacket.

[0042]FIG. 6 is a diagram showing a configuration of a PagingNotification packet.

[0043]FIG. 7 is an example of operation of the packet communicationsystem carried out when in the active mode the mobile host moves fromits home link to a foreign link.

[0044]FIG. 8 is an example of operation of the packet communicationsystem carried out when in the active mode the mobile host sends apacket to the correspondent host.

[0045]FIG. 9 is an example of operation carried out when in the activemode the correspondent host sends a packet to the mobile host before thecorrespondent host receives the Binding Update packet from the mobilehost.

[0046]FIG. 10 is an example of operation carried out when in the activemode the correspondent host sends a packet to the mobile host after thecorrespondent host receives the Binding Update packet from the mobilehost.

[0047]FIG. 11 is an example of operation carried out when in the activemode the mobile host moves between foreign links provided by accessrouters in an area of an identical mobility agent.

[0048]FIG. 14 is an example of operation carried out when in the activemode the mobile host moves to a foreign link provided by an accessrouter in an area of a different mobility agent.

[0049]FIG. 14 is an example of operation carried out when in the activemode the mobile host moves from a foreign link to its home link.

[0050]FIG. 15 is an example of operation of the packet communicationsystem carried out when the operating mode transitions from the activemode to the idle mode.

[0051]FIG. 15 is an example of operation of the packet communicationsystem carried out when in the idle mode the mobile host moves from itshome link to a foreign link.

[0052]FIG. 16 is an example of operation of the packet communicationsystem carried out when the operating mode transitions from the idlemode to the active mode.

[0053]FIG. 17 is an example of operation carried out when in the idlemode the correspondent host sends a packet to the mobile host before thecorrespondent host receives the Binding Update packet from the mobilehost.

[0054]FIG. 18 is an example of operation carried out when in the idlemode the correspondent host sends a packet to the mobile host after thecorrespondent host receives the Binding Update packet from the mobilehost.

[0055]FIG. 19 is an example of operation carried out when in the idlemode the mobile host moves between foreign links provided by accessrouters in an area of an identical mobility agent.

[0056]FIG. 20 is an example of operation carried out when in the idlemode the mobile host moves to a foreign link provided by an accessrouter in an area of a different mobility agent.

[0057]FIG. 21 is an example of operation carried out when in the idlemode the mobile host moves from a foreign link to its home link.

[0058]FIG. 22 is a diagram showing a configuration of a mobility agentused in the packet communication system according to the embodiment ofthe present invention.

[0059]FIGS. 23A and 23B are flow-charts of the operation of the mobilityagent.

[0060]FIG. 24 is a diagram showing a configuration of a mobile host usedin the packet communication system according to the embodiment of thepresent invention.

[0061]FIGS. 25A and 25B show the operation of the mobile host.

[0062]FIG. 26 is a diagram showing a configuration of a home agent usedin the packet communication system according to the embodiment of thepresent invention.

[0063]FIG. 27 is a diagram showing a virtual configuration of a packetcommunication system including a mobile network.

[0064]FIG. 28 is a configuration example of a packet communicationsystem including mobile networks.

[0065]FIG. 29 is a configuration example of a Subnet-prefix BindingUpdate packet.

[0066]FIG. 30 is a configuration example of a Subnet-prefix BindingAcknowledgement packet.

[0067]FIG. 31 is a configuration example of a Subnet-prefix PagingRequest packet.

[0068]FIG. 32 is a configuration example of a Subnet-prefix PagingNotification packet.

[0069]FIG. 33 is an example of operation carried out when in the activemode the mobile network 2 moves from its home link to a foreign link.

[0070]FIG. 34 is an example of operation carried out when in the activemode a stationary host sends a packet to the correspondent host.

[0071]FIG. 35 is an example of operation carried out when in the activemode the correspondent host sends a packet to the stationary host beforethe correspondent host receives the Subnet-prefix Binding Update packetfrom a mobile router.

[0072]FIG. 36 is an example of operation carried out when in the activemode the correspondent host sends a packet to the stationary host afterthe correspondent host receives the Subnet-prefix Binding Update packetfrom the mobile router.

[0073]FIG. 37 is an example of operation carried out when in the activemode the mobile network 2 moves between foreign links provided by accessrouters in an area of an identical mobility agent.

[0074]FIG. 38 is an example of operation carried out when in the activemode the mobile network 2 moves to a foreign link provided by an accessrouter in an area of a different mobility agent.

[0075]FIG. 39 is an example of operation carried out when in the activemode the mobile network 2 moves from a foreign link to its home link.

[0076]FIG. 40 is an example of operation carried out when the operatingmode transitions from the active mode to the idle mode.

[0077]FIG. 41 is an example of operation carried out when in the idlemode the mobile network 2 moves from its home link to a foreign link.

[0078]FIG. 42 is an example of operation carried out when in the idlemode the correspondent host sends a packet to the stationary host beforethe correspondent host receives the Subnet-prefix Binding Update packetfrom the mobile router.

[0079]FIG. 43 is an example of operation carried out when in the idlemode the correspondent host sends a packet to the stationary host afterthe correspondent host receives the Subnet-prefix Binding Update packetfrom the mobile router.

[0080]FIG. 44 is an example of operation carried out when in the idlemode the mobile network 2 moves between foreign links provided by accessrouters in an area of an identical mobility agent.

[0081]FIG. 45 is an example of operation carried out when in the idlemode the mobile network 2 moves to a foreign link provided by an accessrouter in an area of a different mobility agent.

[0082]FIG. 46 is an example of operation carried out when in the idlemode the mobile network 2 moves from a foreign link to its home link.

[0083]FIG. 47 is an example of operation carried out when the operatingmode transitions from the idle mode to the active mode.

[0084]FIG. 48 is an example of operation carried out when the mobilenetwork 1 moves from its home link to a foreign link and when the mobilehost moves from its home link to a foreign link of the mobile network 1.

[0085]FIG. 49 is an example of operation carried out when in the activemode the correspondent host sends a packet to the mobile host.

[0086]FIG. 50 is an example of operation carried out when in the idlemode the correspondent host sends a packet to the mobile host.

[0087]FIG. 51 is an example of operation carried out when the mobilenetwork 1 moves from its home link to a foreign link and when the mobilenetwork 2 moves from its home link to a foreign link.

[0088]FIG. 52 is an example of operation carried out when in the activemode the correspondent host sends a packet to the stationary host.

[0089]FIG. 53 is an example of operation carried out when in the idlemode the correspondent host sends a packet to the stationary host.

[0090]FIG. 54 is a configuration example of a packet communicationsystem including a plurality of mobile networks 1.

[0091]FIG. 55 is an example of operation carried out when the mobilenetworks 1 and the mobile host are connected like chain.

[0092]FIG. 56 is an example of operation carried out when thecorrespondent host sends a packet to the mobile host.

[0093]FIG. 57 is a configuration example of a packet communicationsystem where there exist mobile networks 3 and a mobility agent.

[0094]FIG. 58 is a diagram showing the operation of the mobile hostcarried out after the mobile network has moved to a foreign link andwhen the mobile host moves to the mobile network.

[0095]FIG. 59 is a diagram showing the operation of forwarding a packetaddressed to the mobile host, sent from the correspondent host.

[0096]FIG. 60 is an example of operation carried out when in the activemode the mobile host moves between foreign links provided by accessrouters in an area of an identical mobility agent.

[0097]FIG. 61 is a diagram showing an example of operation of accessrouters belonging to service areas of plural mobility agents.

[0098]FIG. 62 is a diagram showing an example of operation where themobile host uses a plurality of mobility agents.

[0099]FIG. 63 is a diagram showing an example of operation carried outwhen the correspondent host sends a packet addressed to the mobile host.

[0100]FIG. 64 is a diagram showing an example of operation carried outwhen the mobile host moves between areas of mobility agents.

[0101]FIG. 65 is a diagram showing a configuration of a mobile routerused in the packet communication system of the embodiment according tothe present invention.

[0102]FIGS. 66A, 66B and 66C are flow-charts of the operation of themobile router.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0103] Embodiments of the present invention will be described below onthe basis of the drawings.

First Embodiment

[0104]FIG. 2 is a configuration example of a packet communication systemaccording to the present invention. In FIG. 2, HA represents a homeagent, each MA a mobility agent, each AR an access router, MH a MobileHost, and CH a Correspondent Host. Although FIG. 2 shows no router, thenetwork includes an arbitrary number of routers as the packetcommunication system of the prior art did. The packet communicationsystem of the present invention has the configuration obtained by addingthe mobility agents to the packet communication system of the prior art.The mobility agents are routers having functions that will be describedhereinafter, and an arbitrary number of mobility agents exist in thenetwork. Each mobility agent provides a service of relaying a packetfrom the home agent to the mobile host and a packet from thecorrespondent host to the mobile host, for the mobile host located in anarea including one or more access routers. Further, each mobility agentprovides a service of buffering a packet addressed to the mobile host,received from the home agent or from the correspondent host, for themobile host. Each access router is included in an area of at least onemobility agent and functions to notify the mobile host of an address ofthe mobility agent where the mobile host uses a foreign link.

[0105] The packet communication system of the present invention,different from the packet communication system of the prior art, has twooperating modes. One is an idle mode defining a state in which no packetis transmitted between the mobile host and the correspondent host, andthe other an active mode defining a state in which a packet istransmitted between the mobile host and the correspondent host.

[0106]FIG. 3 is a configuration example of a Binding Update packet inthe present invention. The Binding Update packet includes a BindingUpdate option in an option header of an IP packet. The Binding Updateoption is of either a format sent from the mobile host to the mobilityagent or a format sent from the mobile host to the home agent and thecorrespondent host.

[0107] The format for the mobility agent is comprised of an optionidentifier, an option length, a home address, a forwarding destinationaddress, an operating mode, and buffering service on/off. The optionidentifier indicates that the option is Binding Update. The optionlength indicates the length of the option. The home address indicatesthe home address of the mobile host that sends the Binding Updatepacket. The forwarding destination address indicates an address of aforwarding destination of a packet directed to the home address of themobile host, in which a c/o address used at a foreign link by the mobilehost or the home address is set. The operating mode indicates either theidle mode or the active mode. The buffering service on/off indicateswhether the buffering of packet is necessary or not at the mobilityagent.

[0108] The format for the home agent and the correspondent host iscomprised of an option identifier, an option length, a home address, anda forwarding destination address. These are the same as those in theformat for the mobility agent, but the address of the mobility agent orthe home address of the mobile host is set in the forwarding destinationaddress.

[0109] The Binding Update packet is used when the mobile host notifiesthe mobility agent of the binding being a correspondence between thehome address and the c/o address, the operating mode, and the bufferingservice on/off, and is also used when the mobile host notifies the homeagent and the correspondent host of the binding between the home addressand the mobility agent address.

[0110] In FIG. 3, the header includes a destination address, a sourceaddress, and so on. Set in the forwarding destination address is eitherof the c/o address used at the foreign link by the mobile host, themobility agent address, and the home address.

[0111]FIG. 4 is a configuration example of a Binding Acknowledgementpacket in the present invention. The Binding Acknowledgement packetincludes a Binding Acknowledgement option in an option header of an IPpacket. The Binding Acknowledgement option is of either a format sentfrom the mobility agent to the mobile host or a format sent from thehome agent and the correspondent host to the mobile host.

[0112] The format for the mobility agent is comprised of an optionidentifier, an option length, a home address, a forwarding destinationaddress, an operating mode, and buffering service on/off. The optionidentifier indicates that the option is a Binding Acknowledgementoption. The option length indicates the length of the option. The homeaddress, forwarding destination address, operating mode, and bufferingservice on/off are set to the same contents as those in the BindingUpdate packet that the mobility agent received from the mobile host.

[0113] The format for the home agent and the correspondent host iscomprised of an option identifier, an option length, a home address, anda forwarding destination address. These are much the same as those forthe mobility agent.

[0114] The Binding Acknowledgement packet is used when the mobilityagent, the home agent, and the correspondent host notify the mobile hostof completion of processing of the Binding Update packet.

[0115] In FIG. 4, the header includes a destination address, a sourceaddress, and so on. Set in the forwarding destination address is eitherof the c/o address used at the foreign link by the mobile host, themobility agent address, and the home address.

[0116]FIG. 5 is a configuration example of a Paging Request packet inthe present invention. The Paging Request packet is comprised of a homeaddress number (N) of home addresses included in a payload of an IPpacket, and home address 1 to home address N. The home address number(N) indicates the number of home addresses included in the PagingRequest packet. Home address 1 to home address N indicate home addressesof one or more mobile hosts that are requested to receive the PagingRequest packet and to transition from the idle mode to the active mode.

[0117] The Paging Request packet is used when the mobility agentnotifies the access routers in the area of the aforementionedinformation. The addresses of the access routers in the same area areset as destination addresses of the Paging Request packet. The addressesof the access routers in the same area can be unicast addressesdifferent among the access routers or a common multicast address to theaccess routers. In the former case, the mobility agent sends individualPaging Request packets to the respective access routers. In the lattercase, the mobility agent sends one Paging Request packet.

[0118] In FIG. 5, the header includes the destination addresses, thesource address, and so on. The addresses of the access routers are setas the destination addresses of the Paging Request packet.

[0119]FIG. 6 is a configuration example of a Paging Notification packetin the present invention. The Paging Notification packet is comprised ofa home address number (N) of home addresses included in a payload of anIP packet, and home address 1 to home address N. The home address number(N) indicates the number of home addresses included in the PagingNotification packet. Home address 1 to home address N indicate homeaddresses of one or more mobile hosts that are requested to receive thePaging Notification packet and to transition from the idle mode to theactive mode.

[0120] The Paging Notification packet is used when the access routernotifies the mobile host under connection to the foreign link of theforegoing information. Set as destination addresses of the PagingNotification packet are addresses of destinations of all nodes in theforeign link (broadcast addresses).

[0121] In FIG. 6, the header includes the destination addresses, thesource address, and so on. Set as the destination addresses of thePaging Notification packet are the addresses of destinations of all thenodes in the link (broadcast addresses).

[0122]FIG. 7 is an example of operation of the packet communicationsystem carried out when in the active mode the mobile host moves fromits home link to a foreign link. The operation example will be describedbelow on the basis of FIG. 7.

[0123] (1) After the mobile host has moved from the home link to theforeign link, it acquires a c/o address and an address of a mobilityagent from an access router.

[0124] (2) The mobile host sends to the mobility agent the BindingUpdate packet including the binding between the home address and the c/oaddress and indicating that the operating mode is the active mode andthat there is no need for buffering of packet. The mobility agentreceives the Binding Update packet, stores the binding between the homeaddress and the c/o address, the operating mode being the active mode,and no need for buffering of packet, and then is sends the BindingAcknowledgement packet to the mobile host. The mobile host receives theBinding Acknowledgement packet to recognize that the Binding Updatepacket has arrived at the mobility agent and that normal processing isdone.

[0125] (3) The mobile host sends the Binding Update packet including thebinding between the home address and the address of the mobility agentto the home agent. The home agent receives the Binding Update packet,stores the binding between the home address and the mobility agentaddress, and then sends the Binding Acknowledgement packet to the mobilehost. The mobile host receives the Binding Acknowledgement packet torecognize that the Binding Update packet has arrived at the home agentand that normal processing is done.

[0126]FIG. 8 is an example of operation of the packet communicationsystem carried out when in the active mode the mobile host sends apacket to the correspondent host. The operation example will bedescribed below on the basis of FIG. 8.

[0127] The mobile host sends the packet to the correspondent host. Thepacket is routed from the mobile host to the correspondent host by therouters in the network.

[0128]FIG. 9 is an example of operation carried out when in the activemode, before the correspondent host receives the Binding Update packetfrom the mobile host, the correspondent host sends a packet to themobile host. The operation example will be described below on the basisof FIG. 9.

[0129] (1) The correspondent host sends the packet the destination ofwhich is the home address of the mobile host. The packet is routed tothe home link by the routers in the network.

[0130] (2) When the destination of the packet is the home address of thebinding, the home agent of the home link receives the packet instead ofthe mobile host, generates a tunneling packet the destination of whichis the mobility agent address of the binding, puts the received packetinto the payload of the tunneling packet, and sends it. The tunnelingpacket is routed to the mobility agent by the routers in the network.

[0131] (3) The mobility agent receives the tunneling packet from thehome agent and extracts the packet included therein. When thedestination of the packet thus extracted matches with the home addressof the binding, the mobility agent puts the extracted packet into apayload of a tunneling packet whose destination is the c/o address ofthe binding, and sends the tunneling packet. The tunneling packet isrouted to the mobile host by the routers in the network. Receiving thetunneling packet from the mobility agent, the mobile host extracts thepacket from the payload to receive the packet directed to its own homeaddress at last.

[0132] (4) When the mobile host receives the tunneling packet withoutthe routing header in which its home address is set, it determines thatthe correspondent host does not have the binding between the homeaddress and the mobility agent address, and sends to the correspondenthost the Binding Update packet including the binding between the homeaddress and the mobility agent address. The correspondent host receivesthe Binding Update packet and stores the binding between the homeaddress and the mobility agent address.

[0133]FIG. 10 is an example of operation carried out when in the activemode, after the correspondent host receives the Binding Update packetfrom the mobile host, the correspondent host sends a packet to themobile host. The operation example will be described below on the basisof FIG. 10.

[0134] (1) On the occasion of sending the packet directed to the homeaddress indicated by the stored binding, the correspondent host sets thedestination of the packet to the c/o address, puts the routing headeroption with the home address of the binding into the packet, and sendsit. The c/o address of the binding stored at the correspondent host atthis time is the mobility agent address. The packet is routed to themobility agent by the routers in the network.

[0135] (2) The mobility agent receives the packet from the correspondenthost. When the home address included in the routing header optionmatches with the home address of the binding, the mobility agentinterchanges the destination of the packet and the home address includedin the routing header option with each other, puts the packet into thepayload of a tunneling packet whose destination is the c/o address ofthe binding, and sends it. The tunneling packet is routed to the mobilehost by the routers in the network. Receiving the tunneling packet fromthe mobility agent, the mobile host extracts the packet from the payloadto receive the packet directed to its own home address at last.

[0136]FIG. 11 is an example of operation carried out when in the activemode the mobile host moves between foreign links provided by accessrouters in an area of the same mobility agent. The operation examplewill be described below on the basis of FIG. 11.

[0137] (1) Before moving to another foreign link, the mobile host sendsto the mobility agent the Binding Update packet including the bindingbetween the home address and the c/o address and indicating that theoperating mode is the active mode and that the buffering of packet isnecessary. The mobility agent receives the Binding Update packet, storesthe binding between the home address and the c/o address, the operatingmode being the active mode, and the necessity for buffering of packet,and sends the Binding Acknowledgement packet to the mobile host.Receiving the Binding Acknowledgement packet, the mobile host recognizesthat the Binding Update packet has arrived at the mobility agent andthat normal processing is done. After the mobility agent is notified ofthe necessity for buffering of packet by the mobile host and when themobility agent receives an applicable packet from the home agent or thecorrespondent host, it buffers the packet addressed to the mobile host.

[0138] (2) The mobile host moves between foreign links.

[0139] (3) After the mobile host has moved to another foreign link, itacquires a c/o address and an address of a mobility agent from an accessrouter.

[0140] (4) The mobile host judges whether there is change in the addressof the mobility agent. Without change, it sends to the mobility agentthe Binding Update packet including the binding between the home addressand the c/o address and indicating that the operating mode is the activemode and that there is no need for buffering of packet. Receiving theBinding Update packet, the mobility agent stores the binding between thehome address and the c/o address, the operating mode being the activemode, and no necessity for buffering of packet, and then sends theBinding Acknowledgement packet to the mobile host. Receiving the BindingAcknowledgement packet, the mobile host recognizes that the BindingUpdate packet has arrived at the mobility agent and that normalprocessing is done. When the mobility agent bears buffered packets, itsequentially sends the buffered packets to the mobile host according tothe operation similar to FIG. 9 or FIG. 10.

[0141]FIG. 14 is an example of operation carried out when in the activemode the mobile host moves to a foreign link provided by an accessrouter in an area of a different mobility agent. The operation examplewill be described below on the basis of FIG. 14.

[0142] (1) Before moving to another foreign link, the mobile host sendsto the mobility agent the Binding Update packet including the bindingbetween the home address and the c/o address and indicating that theoperating mode is the active mode and that the buffering of packet isnecessary. Receiving the Binding Update packet, the mobility agentstores the binding between the home address and the c/o address, theoperating mode being the active mode, and the necessity for buffering ofpacket, and then sends the Binding Acknowledgement packet to the mobilehost. Receiving the Binding Acknowledgement packet, the mobile hostrecognizes that the Binding Update packet has arrived at the mobilityagent and that normal processing is done. After the mobility agent isnotified of the necessity for buffering of packet by the mobile host andwhen the mobility agent receives an applicable packet from the homeagent or the correspondent host, it buffers the packet addressed to themobile host.

[0143] (2) The mobile host arrives at the foreign link.

[0144] (3) After the mobile host has moved to the other foreign link, itacquires a c/o address and an address of a mobility agent from an accessrouter.

[0145] (4) The mobile host judges whether there is change in the addressof the mobility agent. With change, the mobile host sends to theprevious mobility agent the Binding Update packet including the bindingbetween the home address and the c/o address and indicating that theoperating mode is the active mode and that the buffering of packet isunnecessary. Receiving the Binding Update packet, the previous mobilityagent stores the binding between the home address and the c/o address,the operating mode being the active mode, and no need for buffering ofpacket, and then sends the Binding Acknowledgement packet to the mobilehost. Receiving the Binding Acknowledgement packet, the mobile hostrecognizes that the Binding Update packet has arrived at the previousmobility agent and that normal processing is done. When the mobilityagent bears buffered packets, it sequentially sends the buffered packetsto the mobile host according to the operation similar to FIG. 9 or FIG.10.

[0146] (5) The mobile host sends to the mobility agent the BindingUpdate packet including the binding between the home address and the c/oaddress and indicating that the operating mode is the active mode andthat the buffering of packet is unnecessary. Receiving the BindingUpdate packet, the mobility agent stores the binding between the homeaddress and the c/o address, the operating mode being the active mode,and no need for buffering of packet, and then sends the BindingAcknowledgement packet to the mobile host. Receiving the BindingAcknowledgement packet, the mobile host recognizes that the BindingUpdate packet has arrived at the mobility agent and that normalprocessing is done.

[0147] (6) The mobile host sends to the home agent the Binding Updatepacket including the binding between the home address and the mobilityagent address. Receiving the Binding Update packet, the home agentstores the binding between the home address and the mobility agentaddress and sends the Binding Acknowledgement packet to the mobile host.Receiving the Binding Acknowledgement packet, the mobile host recognizesthat the Binding Update packet has arrived at the home agent and thatnormal processing is done.

[0148] (7) The mobile host sends to the correspondent host the BindingUpdate packet including the binding between the home address and themobility agent address. The correspondent host receives the BindingUpdate packet and stores the Binding between the home address and themobility agent address.

[0149]FIG. 14 is an example of operation carried out when in the activemode the mobile host moves from the foreign link to the home link. Theoperation example will be described below on the basis of FIG. 14.

[0150] (1) The mobile host sends to the mobility agent the BindingUpdate packet including the binding between the home address and thehome address and indicating that the operating mode is the active modeand that the buffering of packet is necessary. Receiving the BindingUpdate packet, the mobility agent stores the binding between the homeaddress and the home address, the operating mode being the active mode,and the need for buffering of packet, and then sends the BindingAcknowledgement packet to the mobile host. Receiving the BindingAcknowledgement packet, the mobile host recognizes that the BindingUpdate packet has arrived at the previous mobility agent and that normalprocessing is done. After the mobility agent is notified of thenecessity for buffering of packet by the mobile host and when themobility agent receives an applicable packet from the home agent or thecorrespondent host, it buffers the packet addressed to the mobile host.

[0151] (2) The mobile host moves from the foreign link to the home link.

[0152] (3) The mobile host acknowledges the movement to the home link.For example, the mobile host can judge the movement from the foreignlink to the home link by receiving Router Advertisement sent from thehome agent.

[0153] (4) The mobile host sends to the home agent the Binding Updatepacket requesting to erase the stored binding between the home addressand the mobility agent address. Receiving the Binding Update packet, thehome agent erases the binding between the home address and the mobilityagent address and sends the Binding Acknowledgement packet to the mobilehost. Thereafter, the home agent stops the operation of receiving apacket instead of the mobile host and forwarding the packet to themobility agent.

[0154] (5) The mobile host sends to the mobility agent used before themovement, the Binding Update packet including the binding between thehome address and the home address and indicating that the operating modeis the active mode and that the buffering of packet is unnecessary.Receiving the Binding Update packet, the mobility agent stores thebinding between the home address and the home address, the operatingmode being the active mode, and no need for buffering of packet, andthen sends the Binding Acknowledgement packet to the mobile host.Receiving the Binding Acknowledgement packet, the mobile host recognizesthat the Binding Update packet has arrived at the previous mobilityagent and that normal processing is done. When the mobility agent bearsbuffered packets, it sequentially sends the buffered packets to themobile host according to the operation similar to FIG. 9 or FIG. 10.

[0155] (6) The mobile host sends to the correspondent host the BindingUpdate packet including the binding between the home address and thehome address. Receiving the Binding Update packet, the correspondenthost deletes the stored Binding between the home address and themobility agent address. Thereafter, the correspondent host sends apacket addressed to the mobile host, in the form of the normal packetwithout the routing header option.

[0156]FIG. 15 is an example of operation of the packet communicationsystem carried out when the operating mode transitions from the activemode to the idle mode. The present operation example is executed whenduring the operating mode of the active mode the mobile host and thecorrespondent host receive or send no packet other than the BindingUpdate packet and the Binding Acknowledgement packet for a predeterminedperiod of time. The operation example will be described below on thebasis of FIG. 15.

[0157] (1) When the mobile host sends or receives no packet to or fromthe correspondent host for the predetermined period, it sends to themobility agent the Binding Update packet including the binding betweenthe home address and the c/o address and indicating that the operatingmode is the idle mode and that the buffering of packet is necessary.Receiving the Binding Update packet, the mobility agent stores thebinding and the operating mode being the idle mode, and then sends theBinding Acknowledgement packet to the mobile host. Receiving the BindingAcknowledgement packet, the mobile host recognizes that the BindingUpdate packet has arrived at the mobility agent and that normalprocessing is done.

[0158] Described on the basis of FIGS. 8 to 15 above were the operationexamples in the active mode of the communication system of the presentinvention. Before moving between foreign links, the mobile host sendsthe Binding Update packet to the mobility agent to make the mobilityagent buffer packets to be forwarded to itself, receives the BindingAcknowledgement packet to receive all the packets addressed to itself,routed to the foreign link now under use, and then moves between foreignlinks. Further, after the movement between foreign links, the mobilehost sends the Binding Update packet to the mobility agent to make themobility agent route buffered packets to the foreign link of the movingdestination. When the same mobility agent is used before and after themovement between the foreign links, the mobile host is required merelyto send the Binding Update packet to only the mobility agent, but doesnot have to send it to the home agent and the correspondent host.

[0159]FIG. 15 is an example of operation of the packet communicationsystem carried out when in the idle mode the mobile host moves from thehome link to a foreign link. The operation example will be describedbelow on the basis of FIG. 15.

[0160] (1) After the mobile host has moved from the home link to theforeign link, it acquires a c/o address and an address of a mobilityagent from an access router.

[0161] (2) The mobile host sends to the mobility agent the BindingUpdate packet including the binding between the home address and the c/oaddress and indicating that the operating mode is the idle mode and thatthe buffering of packet is necessary. Receiving the Binding Updatepacket, the mobility agent stores the binding between the home addressand the c/o address, the operating mode being the idle mode, and theneed for buffering of packet, and then sends the Binding Acknowledgementpacket to the mobile host. Receiving the Binding Acknowledgement packet,the mobile host recognizes that the Binding Update packet has arrived atthe mobility agent and that normal processing is done.

[0162] (3) The mobile host sends to the home agent the Binding Updatepacket including the binding between the home address and the mobilityagent address. Receiving the Binding Update packet, the home agentstores the binding between the home address and the mobility agentaddress and sends the Binding Acknowledgement packet to the mobile host.Receiving the Binding Acknowledgement packet, the mobile host recognizesthat the Binding Update packet has arrived at the home agent and thatnormal processing is done.

[0163]FIG. 16 is an example of operation carried out when in the idlemode, before the correspondent host receives the Binding Update packetfrom the mobile host, the correspondent host sends a packet to themobile host. The operation example will be described below on the basisof FIG. 16.

[0164] (1) The correspondent host sends the packet the destination ofwhich is the home address of the mobile host. The packet is routed tothe home link by the routers in the network.

[0165] (2) When the destination of the packet is the home address of thebinding, the home agent of the home link receives the packet instead ofthe mobile host, generates a tunneling packet the destination of whichis the address of the mobility agent of the binding, puts the receivedpacket into the payload of the tunneling packet, and sends it. Thetunneling packet is routed to the mobility agent by the routers in thenetwork.

[0166] (3) Receiving the tunneling packet from the home agent, themobility agent extracts the packet from the payload. When thedestination of the extracted packet matches with the home address of thebinding, the mobility agent buffers the packet and sends Paging Requestincluding the home address of the mobile host, to the access routers inthe area.

[0167] (4) Receiving the Paging Request from the mobility agent, theaccess routers send to the foreign links Paging Notification in whichthe home address included in the Paging Request is set. The mobile hostreceives the Paging Notification from the access router.

[0168] (5) The mobile host judges whether the received PagingNotification includes its own home address. Without inclusion of thehome address, the mobile host discards the received Paging Notification.With inclusion of the home address, the mobile host sends the BindingUpdate packet including the binding between the home address and the c/oaddress and indicating that the operating mode is the active mode andthat the buffering of packet is unnecessary. The mobility agent receivesthe Binding Update packet, stores the binding between the home addressand the c/o address, the operating mode being the active mode, and noneed for buffering of packet, and then sends the Binding Acknowledgementpacket to the mobile host. Receiving the Binding Acknowledgement packet,the mobile host recognizes that the Binding Update packet has arrived atthe mobility agent and that normal processing is done.

[0169] (6) The mobility agent puts each buffered packet into the payloadof the tunneling packet the destination of which is the c/o address ofthe binding, and sends the tunneling packet. The tunneling packet isrouted to the mobile host by the routers in the network. Receiving thetunneling packet from the mobility agent, the mobile host extracts thepacket from the payload to receive the packet directed to its own homeaddress at last.

[0170]FIG. 17 is an example of operation carried out when in the idlemode, after the correspondent host receives the Binding Update packetfrom the mobile host, the correspondent host sends a packet to themobile host. The operation example will be described below on the basisof FIG. 17.

[0171] (1) When the correspondent host sends the packet directed to thehome address indicated by the stored binding, it sets the c/o address asthe destination of the packet, puts the routing header option in whichthe home address of the binding is set, into the packet, and sends thepacket. The packet is routed to the mobility agent by the routers in thenetwork.

[0172] (2) The mobility agent receives the packet from the correspondenthost. When the home address included in the routing header optionmatches with the home address of the binding, the mobility agentinterchanges the destination of the packet and the home address includedin the routing header option, with each other, buffers the packet, andsends Paging Request including the home address of the mobile host, tothe access routers in the area.

[0173] (3) The access routers receive the Paging Request from themobility agent, and send to the foreign links Paging Notification inwhich the home address included in the Paging Request is set. The mobilehost receives the Paging Notification from the access router.

[0174] (4) The mobile host judges whether the received PagingNotification includes its own home address. Without inclusion of thehome address, the mobile host discards the received Paging Notification.With inclusion of the home address, the mobile host sends the BindingUpdate packet including the binding between the home address and the c/oaddress and indicating that the operating mode is the active mode andthat the buffering of packet is unnecessary. The mobility agent receivesthe Binding Update packet, stores the binding between the home addressand the c/o address, the operating mode being the active mode, and noneed for buffering of packet, and then sends the Binding Acknowledgementpacket to the mobile host. Receiving the Binding Acknowledgement packet,the mobile host recognizes that the Binding Update packet has arrived atthe mobility agent and that normal processing is done.

[0175] (5) The mobility agent puts each buffered packet into the payloadof the tunneling packet the destination of which is the c/o address ofthe binding, and sends the tunneling packet. The tunneling packet isrouted to the mobile host by the routers in the network. Receiving thetunneling packet from the mobility agent, the mobile host extracts thepacket from the payload to receive the packet directed to its own homeaddress at last.

[0176]FIG. 18 is an example of operation carried out when in the idlemode the mobile host moves between foreign links provided by accessrouters in the area of the same mobility agent. The operation examplewill be described below on the basis of FIG. 18.

[0177] (1) The mobile host moves between foreign links.

[0178] (2) After the mobile host has moved to the other foreign link, itacquires a c/o address and an address of a mobility agent from an accessrouter. The mobile host judges whether there is change in the address ofthe mobility agent, and performs nothing without any change.

[0179]FIG. 19 is an example of operation carried out when in the idlemode the mobile host moves to a foreign link provided by an accessrouter in an area of a different mobility agent. The operation examplewill be described below on the basis of FIG. 19.

[0180] (1) The mobile host moves between foreign links.

[0181] (2) After the mobile host has moved to the other foreign link, itacquires a c/o address and an address of a mobility agent from an accessrouter.

[0182] (3) The mobile host judges whether there is change in the addressof the mobility agent. With change, the mobile host sends to themobility agent Binding Update including the binding between the homeaddress and the c/o address and indicating that the operating mode isthe idle mode and that the buffering of packet is necessary. Receivingthe Binding Update, the mobility agent stores the binding between thehome address and the c/o address and the operating mode being the idlemode, and then sends the Binding Acknowledgement packet to the mobilehost. Receiving the Binding Acknowledgement packet, the mobile hostrecognizes that the Binding Update packet has arrived at the mobilityagent and that normal processing is done.

[0183] (4) Further, the mobile host sends to the home agent BindingUpdate including the binding between the home address and the mobilityagent address. Receiving the Binding Update, the home agent stores thebinding between the home address and the mobility agent and then sendsthe Binding Acknowledgement packet to the mobile host. Receiving theBinding Acknowledgement packet, the mobile host recognizes that theBinding Update packet has arrived at the home agent and that normalprocessing is done.

[0184] (5) The mobile host sends to the correspondent host the BindingUpdate packet including the binding between the home address and themobility agent address. Receiving the Binding Update packet, thecorrespondent host stores the Binding between the home address and themobility agent address.

[0185]FIG. 20 is an example of operation carried out when in the idlemode the mobile host moves from the foreign link to the home link. Theoperation example will be described below on the basis of FIG. 20.

[0186] (1) The mobile host moves from the foreign link to the home link.

[0187] (2) The mobile host acknowledges the movement to the home link.For example, the mobile host can judge the movement from the foreignlink to the home link by receiving Router Advertisement sent from thehome agent.

[0188] (3) The mobile host sends to the home agent the Binding Updatepacket requesting to erase the stored binding between the home addressand the mobility agent address. Receiving the Binding Update packet, thehome agent erases the binding between the home address and the mobilityagent address and sends the Binding Acknowledgement packet to the mobilehost. Thereafter, the home agent stops the operation of forwarding thepacket to the mobility agent.

[0189] (4) The mobile host sends to the previous mobility agent theBinding Update packet including the binding between the home address andthe home address and indicating that the operating mode is the activemode and that the buffering of packet is unnecessary. Receiving theBinding Update packet, the previous mobility agent stores the bindingbetween the home address and the home address, the operating mode beingthe active mode, and no need for buffering of packet, and then sends theBinding Acknowledgement packet to the mobile host. Receiving the BindingAcknowledgement packet, the mobile host recognizes that the BindingUpdate packet has arrived at the previous mobility agent and that normalprocessing is done.

[0190] (5) The mobile host sends to the correspondent host the BindingUpdate packet including the binding between the home address and thehome address. Receiving the Binding Update packet, the correspondenthost deletes the stored Binding between the home address and themobility agent address. Thereafter, the correspondent host sends apacket addressed to the mobile host, in the form of the normal packetwithout the routing header option.

[0191]FIG. 21 is an example of operation of the packet communicationsystem carried out when the operating mode transitions from the idlemode to the active mode. The present operation example is executed whenduring the operating mode of the idle mode the mobile host sends apacket to the correspondent host. The operation example will bedescribed below on the basis of FIG. 21.

[0192] (1) The mobile host sends to the mobility agent address theBinding Update packet including the binding between the home address andthe c/o address and indicating that the operating mode is the activemode and that the buffering of packet is unnecessary. Receiving theBinding Update packet, the mobility agent stores the binding between thehome address and the c/o address, the operating mode being the activemode, and no need for buffering of packet, and then sends the BindingAcknowledgement packet to the mobile host. Receiving the BindingAcknowledgement packet, the mobile host recognizes that the BindingUpdate packet has arrived at the mobility agent and that normalprocessing is done.

[0193] Described on the basis of FIGS. 15 to 21 above were the operationexamples in the idle mode of the packet communication system of thepresent invention. When the mobile host moves between foreign linkspresent in an area of one mobility agent, it does not have to send theBinding Update packet to either of the mobility agent, the home agent,and the correspondent host.

[0194] The structures and the operations of mobility agent, mobile hostand host agent for the packet communication system will be explained.

[0195]FIG. 22 is a diagram showing a configuration of the mobilityagent.

[0196] As shown in FIG. 22, the mobility agent MA used in the packetcommunication system comprises a memory 10 for performing storing of abinding and buffering of the received packet, an interface 20 forreceiving a packet from the connected link and sending a packet, signalprocessor 30 for controlling the interface 20 to control Binding UpdatePacket processing and routing thereof. The signal processor 30 forwardsBinding Update Packet received in the interface 20 to the memory 10 andcauses the memory 10 store the Binding Update Packet, and furtherperforms buffering in the memory 10 and sending of the packet bufferedin the memory 10 to link through the interface 30 based on the BindingUpdate Packet stored in the memory 10.

[0197] Next, the operations of the mobility agent in the packetcommunication system as shown in FIG. 22 will be explained referring toFIGS. 23A and 23B. FIGS. 23A and 23B are a flow chart of the operationsof the mobility agent. As shown in FIGS. 23A and 23B, the operation ofthe mobility agent is divided into the operation in reception of BindingUpdate Packet, and the operation in the reception of a tunneling packet.Receiving Binding Update packet from mobile host, the mobility agentstores information relating home address, forwarding destinationaddress, operation mode and whether or not buffering of a packet isnecessary in the memory 10. The signal processor 10 of the mobilityagent sends Binding Acknowledgment Packet indicating the completion ofthe storing to the mobility host which sent Binding Update Packetthrough the interface 20. The mobility agent judges whether or notpacket directed to home address is buffered in the memory 10, and whenthe packet directed to home address is buffered, the mobility agent putsthe packet into a payload of a tunneling packet in which destinationaddress is set as forwarding destination address, original address isset as home address of the mobility agent and send it to mobile hostdesignated by the home address.

[0198] Further when the mobility agent receives a tunneling packet fromthe correspondent host (including mobility agent) or home agent, themobility agent picks up a packet included in the payload of the receivedtunneling packet, searches destination address of the packet from thestored home address and judges the correspondent forwarding destinationaddress, operation mode and whether or not buffering of a packet isnecessary to perform the operations according to the following threecases.

[0199] 1) When the operation mode is active and buffering of a packet isnot necessary;

[0200] The mobility agent puts the packet into a payload of a tunnelpacket in which destination address is set as forwarding destinationaddress, and the original address is set as address of the mobilityagent and send it.

[0201] 2) When the operation mode is active and buffering of a packet isnecessary;

[0202] The mobility agent performs buffering of the received packet.

[0203] 3) When the operation mode is idle and buffering of a packet isnecessary;

[0204] The mobility agent performs buffering of the received packet,puts home address into Paging Request packet and send the Paging RequestPacket to all routers in service area. In this operations of themobility agent, the above stated packet communication system functionsas a whole. FIG. 24 is a diagram showing a configuration of mobile host.As shown in FIG. 24, the mobile host used in the packet communicationsystem comprises a memory 100 for storing information in Binding UpdatePacket including the operation mode of the mobile host, whether or notbuffering to the used mobility agent is necessary, home address, andcorrespondence to c/o address, an inter face 120 for receiving a packetfrom the connected link and sending the packet to a link, and a signalprocessor 130 for controlling the interface 120 and the memory 100 tocontrol Binding Update Packet processing and generation/reception of apacket. The signal processor 130 may perform processing of anapplication executing an application program stored in the memory 100 ofthe mobile host.

[0205]FIGS. 25A and 25B are a flow chart of the operations of the mobilehost.

[0206] As shown in FIGS. 25A and 25B, the operation of the mobile hostis divided into the operation in movement of between links, and theoperation when the mobile host receives Paging Notification Packet.

[0207] In the movement between links, before movement of the mobilehost, the mobile host generates Binding Update packet in which homeaddress is set as home address of the mobile host, forwardingdestination address is set as the currently used c/o address and theoperation mode is set as active, and buffering of a packet is set asnecessary, sends the generated Binding Update Packet to current mobilityagents and receives Binding Update Acknowledgement Packet from themobility agents.

[0208] Next, after the mobile host has moved to another link, the mobilehost obtains new c/0 address in the another link and addresses ofmobility agent and judges whether or not the address of the mobilityagents changes. The mobile host perfumes the following two differentprocesses on the basis of this judgment.

[0209] 1) In the case that the address of the mobility agent does notchange:

[0210] In this case, the mobile host generates Binding Update packet inwhich home address is set as home address of the mobile host, forwardingdestination address is set as new c/o address, operation mode is set asactive, and buffering of a packet is set as no necessary.

[0211] Next, the mobile host sends the Binding Update Packet to newmobility agent and receives Binding Update Acknowledgement packet fromnew mobility agent.

[0212] 2) In the case that the address of the mobility agent changes:

[0213] In this case, the mobile host generates Binding Update packet inwhich home address is set as home address of the mobile host, forwardingdestination address is set as new c/o address, operation mode is set asactive, and buffering of a packet is set as necessary.

[0214] Next, the mobile host sends the Binding Update Packet to newmobility agent and receives Binding Update Acknowledgement packet fromnew mobility agent in response to this sending. At the same time, themobile host generates Binding Update packet in which home address is setas home address of the mobile host, forwarding destination address isset as address of new mobility agent, operation mode is set as active,and buffering of a packet is set as no necessary, and the mobile hostsends the Binding Update Packet to the previous mobility agent andreceives Binding Update Acknowledgement packet showing the conformationof reception of the Binding Update Packet from the previous mobilityagent. And, to home agent, the mobile host generates Binding Updatepacket in which home address is set as home address of the mobile host,and forwarding destination address is set as new c/o address, and themobile host sends the Binding Update Packet to the home agent andreceives Binding Update Acknowledgement packet showing the conformationof reception of the Binding Update Packet from the home agent. It ispossible to set the above forwarding destination address as address ofnew mobility agent. Further, although in the above operation, after thesending of Binding Update Packet to the previous mobility agent usedbefore the movement between links and reception of BindingAcknowledgement Packet from the previous mobility agent used beforemovement between links, sending of Binding Update Packet to home agentand reception of Binding Acknowledgement packet from home agent aresequentially performed, these operations may be performed at the sametime in order to shorten the operation time of the mobile host.

[0215] Next, the operation when the mobile host receives PagingNotification Packet will be explained. As shown in FIGS. 25A and 25B,when the mobile host receives Paging Notification packet, the signalprocessor 130 of the mobile host judges whether or not the destinationof the received Paging Notification Packet matches with home address ofthe mobile host, and when the destination of the received PagingNotification Packet does not match with home address of the mobile host,the mobile host discard the received packet and when the destination ofthe received Paging Notification Packet matches with home address of themobile host, the mobile host sends Binding Update Packet in which homeaddress is bound to c/o address, operation mode is set as active, andbuffering of a packet is set as necessary to mobility agent.

[0216]FIG. 26 is a diagram showing a configuration of home agent. Homeagent used in the packet communication system of the present invention,comprises a memory 210 for performing storing of binding, an interface220 for performing reception of a packet from the connected link andsending of the packet to the link, and a signal processor 230 forcontrolling the interface 220 to control Binding Update Packet processand routing of a packet. The signal processor 230 forwards BindingUpdate Packet received in the interface 220 to the memory 210 to causethe memory 210 store the received Binding Update Packet and furtherperforms sending of the received packet to the link through theinterface 220 on the basis of the Binding stored in the memory 210.

[0217] And, when the home agent HA receives a packet, the home agentjudges whether the destination of the received packet matches with homeaddress of the binding, and when the destination of the received packetmatches with the address of the binding, the home agent receives thepacket in the interface 220 instead of mobile host,. Nest, the mobilehost generates a tunneling packet of which destination is address ofmobility agent of the binding in the signal processor 230 andincorporates the received packet into payload of the tunneling packet.And the mobile host sends the tunneling packet to a link through theinterface 220. Further, when the mobile host receives Binding UpdatePacket requesting to delete the binding between the stored home addressand address of the mobility agent from mobile host, the signal processor230 deletes the blinding between home address of the mobile host stirredin the memory 210 and the mobility agent, and after the deletion of thebinding, sends Binding Acknowledgement Packet to the mobile host throughthe interface 220. In the operation, thereafter, the home agent receivespacket instead of mobile host and does not perform sending operation ofpacket to the mobility agent. Further, receiving Binding Update Packetincluding the correspondence between home address and address ofmobility agent in the interface 220, the home agent HA stores thecorrespondence between the home address and address of mobility agent inthe memory 219 and sends Binding Acknowledgement Packet to mobile hostwhich sent the packet.

[0218] Further, the packet communication system of the prior art has theproblem that it is not ready for mobile networks. An example of a mobilenetwork in the packet communication system of the prior art is presentedin FIG. 27. In FIG. 27, each R indicates a router, HA a home agent, eachAR an access router, each SH a stationary host, and CH a correspondenthost.

[0219] The “mobile network” is a network comprised of a mobile routerand at least one node connected thereto. The mobile router moves fromlink to link while bringing along the mobile network. The mobile routeris configured to regularly exchange information indicating theconnection relation with the routers, access routers, and home agentnecessary for routing processing by the routing protocol such as OSPF(Open Shortest Path First) or BGP (Border Gateway Protocol) as therouters, access routers, and home agent were. Even during a stay at aforeign link, the mobile router exchanges the connection information asif it stays at the home link. This permits a packet addressed to a nodein the mobile network to be routed to the home link of the mobilerouter. The mobile network shown in FIG. 27 includes one mobile routerand two stationary hosts. A stationary host is a node having aninvariant connection relation with the mobile router. The mobile networkmay also include a router and/or a mobile host, without having toinclude only the stationary hosts. When the mobile network moves fromthe home link to a foreign link, the mobile router acquires a c/oaddress used at the foreign link, from an access router and then sends aBinding Update packet including the binding between the home address andthe c/o address, to the home agent. Receiving the Binding Update packetfrom the mobile router, the home agent stores the binding and sends aBinding Acknowledgement packet as an acknowledgement response to themobile router. Receiving the Binding Acknowledgement packet from thehome agent, the mobile router recognizes the storage of the binding atthe home agent. When the correspondent host sends a packet addressed toa stationary host in the mobile network, the packet is routed from thecorrespondent host to the home link by the routers in the network. Thehome agent determines that the next forwarding destination of the packetis the mobile router, based on the exchanged information by the routingprotocol, and receives the packet instead of the mobile router. The homeagent judges whether the destination of the packet coincides with thehome address of the stored binding. Since they discord with each other,the home agent judges the tunneling destination unknown and discards thepacket.

Second Embodiment

[0220]FIG. 28 is a configuration example of a packet communicationsystem including mobile networks according to the present invention. Thepacket communication system of the present invention is comprised of astationary network and mobile networks. In FIG. 28, each SH represents aStationary Host, MH a Mobile Host, CH a Correspondent Host, each MR aMobile Router, each HA a home agent, each MA a Mobility Agent, and eachR a Router. Although not shown in FIG. 28, each of the stationarynetwork and mobile networks includes an arbitrary number of routers asin the packet communication system of the prior art. The stationarynetwork is comprised of home agents, mobility agents, a correspondenthost, and access routers adapted to the mobile networks.

[0221] The home agents provide a service of relaying a packet addressedto a node in a mobile network, to a mobile router or a mobility agent.The mobility agents are routers having the functions describedhereinafter, and an arbitrary number of mobility agents exist in thenetwork. The mobility agents provide a service of relaying a packet sentfrom the home agent to a node in a mobile network and a packet sent fromthe correspondent host to a node in a mobile network, for the mobilenetwork existing in an area including one or more access routers.Further, the mobility agents provide, for a node in a mobile network, aservice of buffering a packet directed to the node, received from thehome agent or the correspondent host. The access routers in thestationary network provide foreign links for the mobile host and themobile networks, and each access router is included in an area of atleast one mobility agent and notifies the mobile router of the addressof the mobility agent. When a destination node of a packet can be judgedas a node in a mobile network, the correspondent host does not send thepacket to the home link, but sends it to the mobility agent. The mobilenetworks are networks moving between foreign links provided by thestationary network or by another mobile network, without changing itsinternal configuration, and the mobile networks are generallycategorized under those with and without foreign links to which a mobilehost or a mobile network can obtain access. Mobile network 1 is a mobilenetwork with foreign links, which includes one mobile router and aplurality of access routers. The mobile router changes connecting linksone after another with movement of the mobile network. The accessrouters in mobile network 1 provide foreign links for the mobile hostand the mobile router of the other mobile network, but do not notify themobile router of the address of the mobility agent in the stationarynetwork.

[0222] On the other hand, mobile network 2 is a mobile network withoutany foreign link, which includes one mobile router and a plurality ofstationary hosts. The stationary hosts do not recognize that they aremoving even during movement of the mobile network 2. The stationaryhosts can be included both in the mobile network 2 and in the mobilenetwork 1.

[0223] As in the case of First Embodiment, the packet communicationsystem of the present invention has two operating modes. One is the idlemode being a state in which no packet is transmitted between the mobilerouter and the correspondent host, and the other is the active modebeing a state in which a packet is transmitted between the mobile routerand the correspondent host.

[0224]FIG. 29 is a configuration example of a Subnet-prefix BindingUpdate packet used by the mobile routers in the present invention. TheSubnet-prefix Binding Update packet includes a Subnet-prefix BindingUpdate option in the option header of the IP packet. The Subnet-prefixBinding Update option is of either a format sent from the mobile routerto the mobility agent or a format sent from the mobile router to thehome agent and the correspondent host.

[0225] The format for the mobility agent is comprised of an optionidentifier, an option length, a Subnet-prefix number (N), NSubnet-prefixes, a forwarding destination address, an operating mode,and buffering service on/off. The option identifier indicates that theoption is Subnet-prefix Binding update. The option length indicates thelength of the option. The Subnet-prefix number indicates the number ofSubnet-prefixes included in the option. The Subnet-prefixes indicateSubnet-prefixes of links included in the mobile network of the mobilerouter sending the Subnet-prefix Binding Update packet. The forwardingdestination address indicates an address of a forwarding destination ofa packet a destination of which is an address matching with aSubnet-prefix included in the mobile network, to which the home addressor a c/o address used at a foreign link by the mobile router is set. Theoperating mode indicates either the idle mode or the active mode. Thebuffering service on/off indicates whether or not the buffering ofpacket is necessary at the mobility agent.

[0226] The format for the home agent and the correspondent host iscomprised of an option identifier, an option length, a Subnet-prefixnumber (N), N Subnet-prefixes, and a forwarding destination address.These are the same as those for the mobility agent, but the address ofthe mobility agent or the home address of the mobile router is set asthe forwarding destination address.

[0227] The Subnet-prefix Binding Update packet is used when the mobilerouter notifies the mobility agent of binding as a correspondencebetween the Subnet-prefixes and the c/o address, the operating mode, andbuffering service on/off, and is also used when the mobile routernotifies the home agent and the correspondent host of binding betweenthe Subnet-prefixes and the address of the mobility agent. The mobilerouter also sends the Binding Update packet described in FirstEmbodiment, as well as the Subnet-prefix Binding Update packet.

[0228] In FIG. 29, the header includes the destination address, thesource address, and so on. Set in the forwarding destination address iseither of the c/o address used at the foreign link by the mobile router,the address of the mobility agent, and the home address.

[0229]FIG. 30 is a configuration example of a Subnet-prefix BindingAcknowledgement packet in the present invention. The Subnet-prefixBinding Acknowledgement packet includes a Subnet-prefix BindingAcknowledgement option in the option header of the IP packet. TheSubnet-prefix Binding Acknowledgement option is of either a format sentfrom the mobility agent to the mobile router or a format sent from thehome agent and the correspondent host to the mobile router.

[0230] The format for the mobility agent is comprised of an optionidentifier, an option length, a Subnet-prefix number (N), NSubnet-prefixes, a forwarding destination address, an operating mode,and buffering service on/off. The option identifier indicates that theoption is the Subnet-prefix Binding Acknowledgement option. The optionlength indicates the length of the option. The Subnet-prefix number,Subnet-prefixes, the forwarding destination address, the operating mode,and buffering service on/off are set to the same contents as those inthe Subnet-prefix Binding Update packet received from the mobile routerby the mobility agent.

[0231] The format for the home agent and the correspondent host iscomprised of an option identifier, an option length, a Subnet-prefixnumber, Subnet-prefixes, and a forwarding destination address. These aremuch the same as those in the format for the mobility agent.

[0232] The Subnet-prefix Binding Acknowledgement packet is used when themobility agent, the home agent, and the correspondent host notify themobile router of completion of processing of the Subnet-prefix BindingUpdate packet. The mobility agent, the home agent, and the correspondenthost also send the Binding Acknowledgement packet described in FirstEmbodiment, as well as the Subnet-prefix Binding Acknowledgement packet.

[0233] In FIG. 30, the header includes the destination address, thesource address, and so on. Set in the forwarding destination address iseither of the c/o address used at the foreign link by the mobile router,the address of the mobility agent, and the home address.

[0234]FIG. 31 is a configuration example of a Subnet-prefix PagingRequest packet in the present invention. The Subnet-prefix PagingRequest packet is comprised of a Subnet-prefix number (N) ofSubnet-prefixes included in the payload of the IP packet, andSubnet-prefix 1 to Subnet-prefix N. The Subnet-prefix number (N)indicates the number of Subnet-prefixes included in the Subnet-prefixPaging Request packet. The Subnet-prefix 1 to Subnet-prefix N indicateone or more mobile routers requested to receive the Subnet-prefix PagingRequest packet and to transition from the idle mode to the active mode;specifically, they indicate the Subnet-prefixes of the links included inthe mobile network to which the mobile router belongs.

[0235] The Subnet-prefix Paging Request packet is used when the mobilityagent notifies the access routers in the area of the aforementionedinformation. Set as destination addresses of the Subnet-prefix PagingNotification packet are the addresses of the access routers in the samearea. The addresses of the access routers in the same area can beunicast addresses different among the access routers or a commonmulticast address thereto. In the former case, the mobility agent sendsindividual Subnet-prefix Paging Request packets to the respective accessrouters. In the latter case, the mobility agent sends one Subnet-prefixPaging Request packet.

[0236] In FIG. 31, the header includes the destination addresses, thesource address, and so on. Set as the destination addresses of theSubnet-prefix Paging Request packet are the addresses of the accessrouters.

[0237]FIG. 32 is a configuration example of a Subnet-prefix PagingNotification packet in the present invention. The Subnet-prefix PagingNotification packet is comprised of a Subnet-prefix number (N) ofSubnet-prefixes included in the payload of the IP packet, andSubnet-prefix 1 to Subnet-prefix N. The Subnet-prefix number (N)indicates the number of Subnet-prefixes included in the Subnet-prefixPaging Notification packet. The Subnet-prefix 1 to Subnet-prefix Nindicate one or more mobile routers requested to receive theSubnet-prefix Paging Notification packet and to transition from the idlemode to the active mode; specifically, they indicate the Subnet-prefixesof the links included in the mobile network to which the mobile routerbelongs. The mobile router captures the Subnet-prefixes of the linksincluded in the belonging mobile network, by the routing protocol suchas OSPF or the like used for routing in the mobile network.

[0238] The Subnet-prefix Paging Notification packet is used when theaccess router notifies the mobile router under connection to its foreignlink of the foregoing information. Set as destination addresses of theSubnet-prefix Paging Notification packet are the addresses ofdestinations of all the nodes in the foreign link (broadcast addresses).

[0239] In FIG. 32, the header includes the destination addresses, thesource address, and so on. Set as the destination addresses of theSubnet-prefix Paging Notification packet are the addresses ofdestinations of all the nodes in the link (broadcast addresses).

[0240]FIG. 33 is an example of operation of the packet communicationsystem carried out when in the active mode the mobile network 2 movesfrom its home link to a foreign link. The operation example will bedescribed below on the basis of FIG. 33.

[0241] (1) After the mobile router has moved from the home link to theforeign link, it acquires a c/o address and an address of a mobilityagent from an access router.

[0242] (2) The mobile router sends to the mobility agent the BindingUpdate packet including the binding between the home address and the c/oaddress and indicating that the operating mode is the active mode andthat the buffering of packet is unnecessary. Receiving the BindingUpdate packet, the mobility agent stores the binding between the homeaddress and the c/o address, the operating mode being the active mode,and no need for buffering of packet, and then sends the BindingAcknowledgement packet to the mobile router. Receiving the BindingAcknowledgement packet, the mobile router recognizes that the BindingUpdate packet has arrived at the mobility agent and that normalprocessing is done. Further, the mobile router sends to the mobilityagent the Subnet-prefix Binding Update packet including the bindingbetween the Subnet-prefixes of the links in the mobile network 2 and thec/o address and indicating that the operating mode is the active modeand that the buffering of packet is unnecessary. The mobile router isinformed of the Subnet-prefixes of the links included in the mobilenetwork 2 by the routing protocol such as OSPF or the like. The mobilityagent receives the Subnet-prefix Binding Update packet, stores thebinding between the Subnet-prefixes and the c/o address, the operatingmode being the active mode, and no need for buffering of packet, andthen sends the Subnet-prefix Binding Acknowledgement packet to themobile router. Receiving the Subnet-prefix Binding Acknowledgementpacket, the mobile router recognizes that the Subnet-prefix BindingUpdate packet has arrived at the mobility agent and that normalprocessing is done.

[0243] (3) The mobile router sends to the home agent the Binding Updatepacket including the binding between the home address and the mobilityagent address. Receiving the Binding Update packet, the home agentstores the binding between the home address and the mobility agentaddress and sends the Binding Acknowledgement packet to the mobilerouter. Receiving the Binding Acknowledgement packet, the mobile routerrecognizes that the Binding Update packet has arrived at the home agentand that normal processing is done. Further, the mobile router sends tothe home agent the Subnet-prefix Binding Update packet including thebinding between the Subnet-prefixes of the links in the mobile network 2and the mobility agent address. Receiving the Subnet-prefix BindingUpdate packet, the home agent stores the binding between theSubnet-prefixes and the mobility agent address and then sends theSubnet-prefix Binding Acknowledgement packet to the mobile router. Themobile router recognizes that the Subnet-prefix Binding Update packethas arrived at the home agent and that normal processing is done.

[0244]FIG. 34 is an example of operation of the packet communicationsystem carried out when in the active mode a packet is transmitted froma stationary host in the mobile network 2 to the correspondent host. Theoperation example will be described below on the basis of FIG. 34.

[0245] The stationary host sends the packet to the correspondent host.The packet is routed from the stationary host to the correspondent hostby the routers in the mobile network 2 and the stationary network.

[0246]FIG. 35 is an example of operation carried out when in the activemode, before the correspondent host receives the Subnet-prefix BindingUpdate packet from the mobile router, the correspondent host sends apacket to the stationary host. The operation example will be describedbelow on the basis of FIG. 35.

[0247] (1) The correspondent host sends the packet the destination ofwhich is the address of the stationary host in the mobile network 2. Thepacket is routed to the home link of the mobile network 2 by the routersin the stationary network.

[0248] (2) When the Subnet-prefixes in the destination of the packet arethose in the binding, the home agent of the home link receives thepacket instead of the mobile router, generates a tunneling packet thedestination of which is the mobility agent address of the binding, putsthe received packet into the payload of the tunneling packet, and sendsthe tunneling packet. The tunneling packet is routed to the mobilityagent by the routers in the stationary network.

[0249] (3) Receiving the tunneling packet from the home agent, themobility agent extracts the packet included therein. When theSubnet-prefixes in the destination of the extracted packet match withthose in the binding, the mobility agent puts the packet into thepayload of a tunneling packet the destination of which is the c/oaddress of the binding, and then sends the tunneling packet. Thetunneling packet is routed to the mobile router by the routers in thestationary network.

[0250] (4) Receiving the tunneling packet from the mobility agent, themobile router extracts the packet from the payload. When theSubnet-prefixes in the destination match with those of the links in themobile network 2, the mobile router sends the packet into the mobilenetwork 2. The packet is routed to the stationary host by the routers inthe mobile network 2. The stationary host receives the packet directedto its own address at last.

[0251] (5) When receiving the tunneling packet, the mobile router sendsto the correspondent host the Subnet-prefix Binding Update packetincluding the binding between the Subnet-prefixes and the mobility agentaddress. The correspondent host receives the Subnet-prefix BindingUpdate packet and stores the binding between the Subnet-prefixes and themobility agent address.

[0252]FIG. 36 is an example of operation carried out when in the activemode, after the correspondent host receives the Subnet-prefix BindingUpdate packet from the mobile router, the correspondent host sends apacket to the stationary host. The operation example will be describedbelow on the basis of FIG. 36.

[0253] (1) When the correspondent host sends the packet theSubnet-prefixes in the destination address of which are the same asthose indicated by the stored binding, it sends the packet thedestination of which is the c/o address and which includes the routingheader option in which the home address of the binding is set. Thepacket is routed to the mobility agent by the routers in the stationarynetwork.

[0254] (2) The mobility agent receives the packet from the correspondenthost. When the Subnet-prefixes in the destination address in the routingheader option match with those in the binding, the mobility agentinterchanges the destination of the packet and the destination addressincluded in the routing header option, with each other, puts the packetinto the payload of the tunneling packet the destination of which is thec/o address of the binding, and sends the tunneling packet. Thetunneling packet is routed to the mobile router by the routers in thestationary network.

[0255] (3) Receiving the tunneling packet from the mobility agent, themobile router extracts the packet from the payload. When theSubnet-prefixes in the destination match with those of the links in themobile network 2, the packet is sent into the mobile network 2. Thepacket is routed to the stationary host by the routers in the mobilenetwork 2. The stationary host receives the packet directed to its ownaddress at last.

[0256]FIG. 37 is an example of operation carried out when in the activemode the mobile router in the mobile network 2 moves between foreignlinks provided by access routers in the area of the same mobility agent.The operation example will be described below on the basis of FIG. 37.

[0257] (1) Before moving to another foreign link, the mobile routersends to the mobility agent the Binding Update packet including thebinding between the home address and the c/o address and indicating thatthe operating mode is the active mode and that the buffering of packetis necessary. Receiving the Binding Update packet, the mobility agentstores the binding between the home address and the c/o address, theoperating mode being the active mode, and the need for buffering ofpacket, and then sends the Binding Acknowledgement packet to the mobilerouter. Receiving the Binding Acknowledgement packet, the mobile routerrecognizes that the Binding Update packet has arrived at the mobilityagent and that normal processing is done. Further, before moving to theother foreign link, the mobile router also sends to the mobility agentthe Subnet-prefix Binding Update packet including the binding betweenthe Subnet-prefixes of the links included in the mobile network 2 andthe c/o address and indicating that the operating mode is the activemode and that the buffering of packet is necessary. Receiving theSubnet-prefix Binding Update packet, the mobility agent stores thebinding between the Subnet-prefixes and the c/o address, the operatingmode being the active mode, and the need for buffering of packet, andthen sends the Subnet-prefix Binding Acknowledgement packet to themobile router. Receiving the Subnet-prefix Binding Acknowledgementpacket, the mobile router recognizes that the Subnet-prefix BindingUpdate packet has arrived at the mobility agent and that normalprocessing is done.

[0258] (2) The mobile router moves between foreign links.

[0259] (3) After the mobile router has moved to another foreign link, itacquires a c/o address and an address of a mobility agent from an accessrouter.

[0260] (4) The mobile router judges whether there is change in theaddress of the mobility agent. Without change, the mobile router sendsto the mobility agent the Binding Update packet including the bindingbetween the home address and the c/o address and indicating theoperating mode is the active mode and that the buffering of packet isunnecessary. Receiving the Binding Update packet, the mobility agentstores the binding between the home address and the c/o address, theoperating mode being the active mode, and no need for buffering ofpacket, and then sends the Binding Acknowledgement packet to the mobilerouter. Receiving the Binding Acknowledgement packet, the mobile routerrecognizes that the Binding Update packet has arrived at the mobilityagent and that normal processing is done. Further, the mobile routersends to the mobility agent the Subnet-prefix Binding Update packetincluding the binding between the Subnet-prefixes of the links includedin the mobile network 2 and the c/o address and indicating that theoperating mode is the active mode and that the buffering of packet isunnecessary. Receiving the Subnet-prefix Binding Update packet, themobility agent stores the binding between the Subnet-prefixes and thec/o address, the operating mode being the active mode, and no need forbuffering of packet, and then sends the Subnet-prefix BindingAcknowledgement packet to the mobile router. Receiving the Subnet-prefixBinding Acknowledgement packet, the mobile router recognizes that theSubnet-prefix Binding Update packet has arrived at the mobility agentand that normal processing is done.

[0261]FIG. 38 is an example of operation carried out when in the activemode the mobile router moves to a foreign link provided by an accessrouter in an area of a different mobility agent. The operation examplewill be described below on the basis of FIG. 38.

[0262] (1) Before moving to another foreign link, the mobile routersends to the mobility agent the Binding Update packet including thebinding between the home address and the c/o address and indicating thatthe operating mode is the active mode and that the buffering of packetis necessary. Receiving the Binding Update packet, the mobility agentstores the binding between the home address and the c/o address, theoperating mode being the active mode, and the necessity for buffering ofpacket, and then sends the Binding Acknowledgement packet to the mobilerouter. Receiving the Binding Acknowledgement packet, the mobile routerrecognizes that the Binding Update packet has arrived at the mobilityagent and that normal processing is done. Before moving to the otherforeign link, the mobile router further sends to the mobility agent theSubnet-prefix Binding Update packet including the binding between theSubnet-prefixes of the links included in the mobile network 2 and thec/o address and indicating that the operating mode is the active modeand that the buffering of packet is necessary. Receiving theSubnet-prefix Binding Update packet, the mobility agent stores thebinding between the Subnet-prefixes and the c/o address, the operatingmode being the active mode, and the necessity for buffering of packet,and then sends the Subnet-prefix Binding Acknowledgement packet to themobile router. Receiving the Subnet-prefix Binding Acknowledgementpacket, the mobile router recognizes that the Subnet-prefix BindingUpdate packet has arrived at the mobility agent and that normalprocessing is done.

[0263] (2) The mobile router moves between foreign links.

[0264] (3) After the mobile router has arrived at the other foreignlink, it acquires a c/o address and an address of a mobility agent froman access router.

[0265] (4) The mobile router judges whether there is change in themobility agent address. With change, the mobile router sends to theprevious mobility agent the Binding Update packet including the bindingbetween the home address and the c/o address and indicating that theoperating mode is the active mode and that the buffering of packet isunnecessary. Receiving the Binding Update packet, the previous mobilityagent stores the binding between the home address and the c/o address,the operating mode being the active mode, and no need for buffering ofpacket, and then sends the Binding Acknowledgement packet to the mobilerouter. Receiving the Binding Acknowledgement packet, the mobile routerrecognizes that the Binding Update packet has arrived at the previousmobility agent and that normal processing is done. The mobile routerfurther sends to the previous mobility agent the Subnet-prefix BindingUpdate packet including the binding between the Subnet-prefixes of themobile network 2 and the c/o address and indicating that the operatingmode is the active mode and that the buffering of packet is unnecessary.Receiving the Subnet-prefix Binding Update packet, the previous mobilityagent stores the binding between the Subnet-prefixes and the c/oaddress, the operating mode being the active mode, and no need forbuffering of packet, and then sends the Subnet-prefix BindingAcknowledgement packet to the mobile router. Receiving the Subnet-prefix Binding Acknowledgement packet, the mobile router recognizes thatthe Subnet-prefix Binding Update packet has arrived at the previousmobility agent and that normal processing is done.

[0266] (5) The mobile router sends to the mobility agent the BindingUpdate packet including the binding between the home address and the c/oaddress and indicating that the operating mode is the active mode andthat there is no need for buffering of packet. Receiving the BindingUpdate packet, the mobility agent stores the binding between the homeaddress and the c/o address, the operating mode being the active mode,and no need for buffering of packet, and then sends the BindingAcknowledgement packet to the mobile router. Receiving the BindingAcknowledgement packet, the mobile router recognizes that the BindingUpdate packet has arrived at the mobility agent and that normalprocessing is done. The mobile router further sends to the mobilityagent the Subnet-prefix Binding Update packet including the bindingbetween the Subnet-prefixes of the links included in the mobile network2 and the c/o address and indicating that the operating mode is theactive mode and that there is no need for buffering of packet. Receivingthe Subnet-prefix Binding Update packet, the mobility agent stores thebinding between the Subnet-prefixes and the c/o address, the operatingmode being the active mode, and no need for buffering of packet, andthen sends the Subnet-prefix Binding Acknowledgement packet to themobile router. Receiving the Subnet-prefix Binding Acknowledgementpacket, the mobile router recognizes that the Binding Update packet hasarrived at the mobility agent and that normal processing is done.

[0267] (6) The mobile router sends to the home agent the Binding Updatepacket including the binding between the home address and the address ofthe mobility agent. Receiving the Binding Update packet, the home agentstores the binding between the home address and the c/o address andsends the Binding Acknowledgement packet to the mobile router. Receivingthe Binding Acknowledgement packet, the mobile router recognizes thatthe Binding Update packet has arrived at the home agent and that normalprocessing is done. The mobile router further sends to the home agentthe Subnet-prefix Binding Update packet including the binding betweenthe Subnet-prefixes of the links included in the mobile network 2 andthe mobility agent address. Receiving the Subnet-prefix Binding Updatepacket, the home agent stores the binding between the Subnet-prefixesand the mobility agent address and sends the Subnet-prefix BindingAcknowledgement packet to the mobile router. Receiving the Subnet-prefixBinding Acknowledgement packet, the mobile router recognizes that theSubnet-prefix Binding Update packet has arrived at the home agent andthat normal processing is done.

[0268] (7) The mobile router sends to the correspondent host the BindingUpdate packet including the binding between the home address and themobility agent address. Receiving the Binding Update packet, thecorrespondent host stores the Binding between the home address and themobility agent address. The mobile router further sends to thecorrespondent host the Subnet-prefix Binding Update packet including thebinding between the Subnet-prefixes of the links included in the mobilenetwork 2 and the mobility agent address. Receiving the Subnet-prefixBinding Update packet, the correspondent host stores the binding betweenthe Subnet-prefixes and the mobility agent address.

[0269]FIG. 39 is an example of operation carried out when in the activemode the mobile router moves from the foreign link to the home link. Theoperation example will be described below on the basis of FIG. 39.

[0270] (1) The mobile router sends to the mobility agent the BindingUpdate packet including the binding between the home address and thehome address and indicating that the operating mode is the active modeand that the buffering of packet is necessary. Receiving the BindingUpdate packet, the mobility agent stores the binding between the homeaddress and the home address, the operating mode being the active mode,and the necessity for buffering of packet, and then sends the BindingAcknowledgement packet to the mobile router. Receiving the BindingAcknowledgement packet, the mobile router recognizes that the BindingUpdate packet has arrived at the previous mobility agent and that normalprocessing is done. The mobile router further sends to the mobilityagent the Subnet-prefix Binding Update packet including the bindingbetween the Subnet-prefixes of the links included in the mobile network2 and the home address and indicating that the operating mode is theactive mode and that the buffering of packet is necessary. Receiving theSubnet-prefix Binding Update packet, the mobility agent stores thebinding between the Subnet-prefixes and the home address, the operatingmode being the active mode, and the necessity for buffering of packet,and then sends the Subnet-prefix Binding Acknowledgement packet to themobile router. Receiving the Subnet-prefix Binding Acknowledgementpacket, the mobile router recognizes that the Subnet-prefix BindingUpdate packet has arrived at the previous mobility agent and that normalprocessing is done.

[0271] (2) The mobile router moves from the foreign link to the homelink.

[0272] (3) The mobile router recognizes that it has moved to the homelink. For example, the mobile router judges that it has moved from theforeign link to the home link, by receiving Router Advertisement sentfrom the home agent.

[0273] (4) The mobile router sends to the home agent the Binding Updatepacket requesting to erase the stored binding between the home addressand the mobility agent address. Receiving the Binding Update packet, thehome agent erases the binding between the home address and the mobilityagent address and sends the Binding Acknowledgement packet to the mobilerouter. Thereafter, the home agent stops performing the operation ofreceiving the packet instead of the mobile router and forwarding thepacket to the mobility agent. The mobile router further sends to thehome agent the Subnet-prefix Binding Update packet requesting to erasethe stored binding between the Subnet-prefixes and the mobility agentaddress. Receiving the Subnet-prefix Binding Update packet, the homeagent erases the binding between the Subnet-prefixes and the mobilityagent address and sends the Subnet-prefix Binding Acknowledgement packetto the mobile router. Thereafter, the home agent stops performing theoperation of receiving the packet instead of the mobile router andforwarding the packet to the mobility agent.

[0274] (5) The mobile router sends to the mobility agent previously usedbefore the movement, the Binding Update packet including the bindingbetween the home address and the home address and indicating that theoperating mode is the active mode and that there is no need for thebuffering of packet. Receiving the Binding Update packet, the mobilityagent stores the binding between the home address and the home address,the operating mode being the active mode, and no need for the bufferingof packet, and then sends the Binding Acknowledgement packet to themobile router. Receiving the Binding Acknowledgement packet, the mobilerouter recognizes that the Binding Update packet has arrived at theprevious home agent and that normal processing is done. The mobilerouter further sends to the mobility agent previously used before themovement, the Subnet-prefix Binding Update packet including the bindingbetween the Subnet-prefixes of the links included in the mobile network2 and the home address and indicating that the operating mode is theactive mode and that there is no need for the buffering of packet.Receiving the Subnet-prefix Binding Update packet, the mobility agentstores the binding between the Subnet-prefixes and the home address, theoperating mode being the active mode, and no need for the buffering ofpacket, and then sends the Subnet-prefix Binding Acknowledgement packetto the mobile router. Receiving the Subnet-prefix BindingAcknowledgement packet, the mobile router recognizes that the BindingUpdate packet has arrived at the previous home agent and that normalprocessing is done.

[0275] (6) The mobile router sends to the correspondent host the BindingUpdate packet including the binding between the home address and thehome address. Receiving the Binding Update packet, the correspondenthost deletes the stored Binding between the home address and themobility agent address. The mobile router further sends to thecorrespondent host the Subnet-prefix Binding Update packet including thebinding between the Subnet-prefixes of the links included in the mobilenetwork 2 and the home address. Receiving the Subnet-prefix BindingUpdate packet, the correspondent host deletes the binding between theSubnet-prefixes and the mobility agent address.

[0276]FIG. 40 is an example of operation of the packet communicationsystem carried out when the operating mode transitions from the activemode to the idle mode. When during the operating mode of the active modethere is no packet other than the Binding Update packet, the BindingAcknowledgement packet, the Subnet-prefix Binding Update packet, and theSubnet-prefix Binding Acknowledgement packet transmitted between themobile router and the stationary network for a predetermined period oftime, the present operation example is executed. The operation examplewill be described below on the basis of FIG. 40.

[0277] (1) When the mobile router sends or receives no packet to or fromthe stationary network for the predetermined period, it sends to themobility agent the Binding Update packet including the binding betweenthe home address and the c/o address and indicating that the operatingmode is the idle mode and that the buffering of packet is necessary.Receiving the Binding Update packet, the mobility agent stores thebinding and the operating mode being the idle mode, and then sends theBinding Acknowledgement packet to the mobile router. Receiving theBinding Acknowledgement packet, the mobile router recognizes that theBinding Update packet has arrived at the mobility agent and that normalprocessing is done. The mobile router further sends to the mobilityagent the Subnet-prefix Binding Update packet including the bindingbetween the Subnet-prefixes of the links included in the mobile network2 and the c/o address and indicating that the operating mode is the idlemode and that the buffering of packet is necessary. Receiving theSubnet-prefix Binding Update packet, the mobility agent stores thebinding and the operating mode being the idle mode, and then sends theSubnet-prefix Binding Acknowledgement packet to the mobile router.Receiving the Subnet-prefix Binding Acknowledgement packet, the mobilerouter recognizes that the Subnet-prefix Binding Update packet hasarrived the mobility agent and that normal processing is done.

[0278]FIG. 41 is an example of operation of the packet communicationsystem carried out when in the idle mode the mobile network 2 moves fromthe home link to a foreign link. The operation example will be describedbelow on the basis of FIG. 41.

[0279] (1) After the mobile router has moved from the home link to theforeign link, it acquires a c/o address and an address of a mobilityagent from an access router.

[0280] (2) The mobile router sends to the mobility agent the BindingUpdate packet including the binding between the home address and the c/oaddress and indicating that the operating mode is the idle mode and thatthe buffering of packet is necessary. Receiving the Binding Updatepacket, the mobility agent stores the binding between the home addressand the c/o address, the operating mode being the idle mode, and theneed for the buffering of packet, and then sends the BindingAcknowledgement packet to the mobile router. Receiving the BindingAcknowledgement packet, the mobile router recognizes that the BindingUpdate packet has arrived at the mobility agent and that normalprocessing is done. The mobile router further sends to the mobilityagent the Subnet-prefix Binding Update packet including the bindingbetween the Subnet-prefixes of the links in the mobile network 2 and thec/o address and indicating that the operating mode is the idle mode andthat the buffering of packet is necessary. The mobile router is informedof the Subnet-prefixes of the links included in the mobile network 2, bythe routing protocol such as OSPF or the like. Receiving theSubnet-prefix Binding Update packet, the mobility agent stores thebinding between the Subnet-prefixes and the c/o address, the operatingmode being the idle mode, and the need for the buffering of packet, andthen sends the Subnet-prefix Binding Acknowledgement packet to themobile router. Receiving the Subnet-prefix Binding Acknowledgementpacket, the mobile router recognizes that the Subnet-prefix BindingUpdate packet has arrived at the mobility agent and that normalprocessing is done.

[0281] (3) The mobile router sends to the home agent the Binding Updatepacket including the binding between the home address and the mobilityagent address. Receiving the Binding Update packet, the home agentstores the binding between the home address and the mobility agentaddress and then sends the Binding Acknowledgement packet to the mobilerouter. Receiving the Binding Acknowledgement packet, the mobile routerrecognizes that the Binding Update packet has arrived at the home agentand that normal processing is done. The mobile router further sends tothe home agent the Subnet-prefix Binding Update packet including thebinding between the Subnet-prefixes of the links in the mobile network 2and the mobility agent address. Receiving the Subnet-prefix BindingUpdate packet, the home agent stores the binding between theSubnet-prefixes and the mobility agent address and then sends theSubnet-prefix Binding Acknowledgement packet to the mobile router.Receiving the Subnet-prefix Binding Acknowledgement packet, the mobilerouter recognizes that the Subnet-prefix Binding Update packet hasarrived at the home agent and that normal processing is done.

[0282] Described on the basis of FIGS. 38 to 44 above were the operationexamples in the active mode of the packet communication system accordingto the present invention. The mobile router sends the Binding Updatepacket and the Subnet-prefix Binding Update packet to the mobility agentbefore movement between foreign links to make the mobility agent bufferpackets to be forwarded to the nodes in the mobile network 2, and themobile router receives the Subnet-prefix Binding Acknowledgement packetwhereby it can receive all the packets addressed to the nodes in themobile network 2, routed to the foreign link now under use, andthereafter move between foreign links. Further, the mobile router sendsthe Binding Update packet and the Subnet-prefix Binding Update packet tothe mobility agent after the movement between foreign links whereby themobile router can make buffered packets routed to the foreign link ofthe moving destination. When the same mobility agent is used before andafter the movement between foreign links, the mobile router is requiredmerely to send the Binding Update packet and the Subnet-prefix BindingUpdate packet to only the mobility agent, but does not have to send themto the home agent and the correspondent host.

[0283]FIG. 42 is an example of operation carried out when in the idlemode, before the correspondent host receives the Subnet-prefix BindingUpdate packet from the mobile router, the correspondent host sends apacket to the stationary host. The operation example will be describedbelow on the basis of FIG. 42.

[0284] (1) The correspondent host sends the packet the destination ofwhich is the address of the stationary host in the mobile network 2. Thepacket is routed to the home link of the mobile network 2 by the routersin the stationary network.

[0285] (2) When the Subnet-prefixes in the destination of the packet arethose in the binding, the home agent of the home link receives thepacket instead of the mobile router, generates a tunneling packet thedestination of which is the mobility agent address of the binding, putsthe received packet into the payload of the tunneling packet, and sendsit. The tunneling packet is routed to the mobility agent by the routersin the stationary network.

[0286] (3) The mobility agent receives the tunneling packet from thehome agent and extracts the packet from the payload. When thedestination of the extracted packet matches with the Subnet-prefixes ofthe binding, the mobility agent buffers the packet and sends theSubnet-prefix Paging Request including the Subnet-prefixes, to theaccess routers in the area.

[0287] (4) Receiving the Subnet-prefix Paging Request from the mobilityagent, the access routers send to their foreign links the Subnet-prefixPaging Notification in which the home address included in theSubnet-prefix Paging Request is set. The mobile router receives theSubnet-prefix Paging Notification from the access router.

[0288] (5) The mobile router judges whether the received Subnet-prefixPaging Notification includes the Subnet-prefixes of the links in thebelonging mobile network 2. Without inclusion, the mobile routerdiscards the received Subnet-prefix Paging Notification. With inclusion,the mobile router sends the Subnet-prefix Binding Update packetincluding the binding between the Subnet-prefixes and the c/o addressand indicating that the operating mode is the active mode and that thereis no need for the buffering of packet. Receiving the Subnet-prefixBinding Update packet, the mobility agent stores the binding between theSubnet-prefixes and the c/o address, the operating mode being the activemode, and no need for the buffering of packet, and then sends theSubnet-prefix Binding Acknowledgement packet to the mobile router.Receiving the Subnet-prefix Binding Acknowledgement packet, the mobilerouter recognizes that the Subnet-prefix Binding Update packet hasarrived at the mobility agent and that normal processing is done.

[0289] (6) The mobility agent puts each buffered packet into the payloadof a tunneling packet the destination of which is the c/o address of thebinding, and then sends it. The tunneling packet is routed to the mobilerouter by the routers in the stationary network.

[0290] (7) Receiving the tunneling packet from the mobility agent, themobile router extracts the packet from the payload. When theSubnet-prefixes in the destination match with those of the links in themobile network 2, the mobile router sends the packet into the mobilenetwork 2. The packet is routed to the stationary host by the routers inthe mobile network 2. The stationary host receives the packet directedto its own address at last.

[0291]FIG. 43 is an example of operation carried out when in the idlemode, after the correspondent host receives the Subnet-prefix BindingUpdate packet from the mobile router, the correspondent host sends apacket to the stationary host. The operation example will be describedbelow on the basis of FIG. 43.

[0292] (1) When the correspondent host sends the packet theSubnet-prefixes in the destination address of which are the same asthose indicated by the stored binding, it sets the c/o address as thedestination of the packet, puts the routing header option in which thehome address of the binding is set, into the packet, and then sends it.The packet is routed to the mobility agent by the routers in thestationary network.

[0293] (2) Receiving the tunneling packet from the correspondent host,the mobility agent extracts the packet from the payload. When thedestination of the extracted packet matches with the Subnet-prefixes ofthe binding, the mobility agent buffers the packet and sends theSubnet-prefix Paging Request including the Subnet-prefixes, to theaccess routers in the area.

[0294] (3) Receiving the Subnet-prefix Paging Request from the mobilityagent, the access routers send to their foreign links the Subnet-prefixPaging Notification in which the home address included in theSubnet-prefix Paging Request is set. The mobile router receives theSubnet-prefix Paging Notification from the access router.

[0295] (4) The mobile router judges whether the received Subnet-prefixPaging Notification includes the Subnet-prefixes of the links in thebelonging mobile network 2. Without inclusion, the mobile routerdiscards the received Subnet-prefix Paging Notification. With inclusion,the mobile router sends the Subnet-prefix Binding Update packetincluding the binding between the Subnet-prefixes and the c/o addressand indicating that the operating mode is the active mode and that thereis no need for the buffering of packet. Receiving the Subnet-prefixBinding Update packet, the mobility agent stores the binding between theSubnet-prefixes and the c/o address, the operating mode being the activemode, and no need for the buffering of packet, and then sends theSubnet-prefix Binding Acknowledgement packet to the mobile router.Receiving the Subnet-prefix Binding Acknowledgement packet, the mobilerouter recognizes that the Subnet-prefix Binding Update packet hasarrived at the mobility agent and that normal processing is done.

[0296] (5) The mobility agent puts each buffered packet into the payloadof a tunneling packet the destination of which is the c/o address of thebinding, and sends it. The tunneling packet is routed to the mobilerouter by the routers in the stationary network.

[0297] (6) Receiving the tunneling packet from the mobility agent, themobile router extracts the packet from the payload. When theSubnet-prefixes in the destination match with those of the links in themobile network 2, the mobile router sends the packet into the mobilenetwork 2. The packet is routed to the stationary host by the routers inthe mobile network 2. The stationary host receives the packet directedto its own address at last.

[0298]FIG. 44 is an example of operation carried out when in the idlemode the mobile router moves between foreign links provided by accessrouters in the area of the same mobility agent. The operation examplewill be described below on the basis of FIG. 44.

[0299] (1) The mobile router moves between foreign links.

[0300] (2) After the mobile router has moved to another foreign link, itacquires a c/o address and an address of a mobility agent from an accessrouter. The mobile router judges whether there is change in the mobilityagent address, and performs nothing without any change of the mobilityagent address.

[0301]FIG. 45 is an example of operation carried out when in the idlemode the mobile router moves to a foreign link provided by an accessrouter in an area of a different mobility agent. The operation examplewill be described below on the basis of FIG. 45.

[0302] (1) The mobile router moves between foreign links.

[0303] (2) After the mobile router has moved to another foreign link, itacquires a c/o address and an address of a mobility agent from an accessrouter.

[0304] (3) The mobile router judges whether there is change in themobility agent address. With change, the mobile router sends to themobility agent the Binding Update packet including the binding betweenthe home address and the c/o address and indicating that the operatingmode is the idle mode and that the buffering of packet is necessary.Receiving the Binding Update packet, the mobility agent stores thebinding between the home address and the c/o address, the operating modebeing the idle mode, and the need for the buffering of packet, and thensends the Binding Acknowledgement packet to the mobile router. Receivingthe Binding Acknowledgement packet, the mobile router recognizes thatthe Binding Update packet has arrived at the mobility agent and thatnormal processing is done. The mobile router further sends to themobility agent the Subnet-prefix Binding Update packet including thebinding between the Subnet-prefixes of the links included in the mobilenetwork 2 and the c/o address and indicating that the operating mode isthe idle mode and that the buffering of packet is necessary. Receivingthe Subnet-prefix Binding Update packet, the mobility agent stores thebinding between the Subnet-prefixes and the c/o address, the operatingmode being the idle mode, and the need for the buffering of packet, andthen sends the Subnet-prefix Binding Acknowledgement packet to themobile router. Receiving the Subnet-prefix Binding Acknowledgementpacket, the mobile router recognizes that the Binding Update packet hasarrived at the mobility agent and that normal processing is done.

[0305] (4) The mobile router sends to the home agent the Binding Updatepacket including the binding between the home address and the mobilityagent address. Receiving the Binding Update packet, the home agentstores the binding between the home address and the c/o address andsends the Binding Acknowledgement packet to the mobile router. Receivingthe Binding Acknowledgement packet, the mobile router recognizes thatthe Binding Update packet has arrived at the home agent and that normalprocessing is done. The mobile router further sends to the home agentthe Subnet-prefix Binding Update packet including the binding betweenthe Subnet-prefixes of the links included in the mobile network 2 andthe mobility agent address. Receiving the Subnet-prefix Binding Updatepacket, the home agent stores the binding between the Subnet-prefixesand the c/o address and sends the Subnet-prefix Binding Acknowledgementpacket to the mobile router. Receiving the Subnet-prefix BindingAcknowledgement packet, the mobile router recognizes that theSubnet-prefix Binding Update packet has arrived at the home agent andthat normal processing is done.

[0306] (5) The mobile router sends to the correspondent host the BindingUpdate packet including the binding between the home address and themobility agent address. Receiving the Binding Update packet, thecorrespondent host stores the Binding between the home address and themobility agent address. The mobile router further sends to thecorrespondent host the Subnet-prefix Binding Update packet including thebinding between the Subnet-prefixes of the links included in the mobilenetwork 2 and the mobility agent address. Receiving the Subnet-prefixBinding Update packet, the correspondent host stores the binding betweenthe Subnet-prefixes and the mobility agent address.

[0307]FIG. 46 is an example of operation carried out when in the idlemode the mobile router moves from the foreign link to the home link. Theoperation example will be described below on the basis of FIG. 46.

[0308] (1) The mobile router moves from the foreign link to the homelink.

[0309] (2) The mobile router recognizes that it has moved to the homelink. For example, the mobile router can judge that it has moved fromthe foreign link to the home link, by receiving Router Advertisementsent from the home agent.

[0310] (3) The mobile router sends to the home agent the Binding Updatepacket requesting to erase the stored binding between the home addressand the mobility agent address. Receiving the Binding Update packet, thehome agent erases the binding between the home address and the mobilityagent address and sends the Binding Acknowledgement packet to the mobilerouter. Thereafter, the home agent stops performing the operation ofreceiving the packet instead of the mobile router and forwarding thepacket to the mobility agent. The mobile router further sends to thehome agent the Subnet-prefix Binding Update packet requesting to erasethe stored binding between the Subnet-prefixes and the mobility agentaddress. Receiving the Subnet-prefix Binding Update packet, the homeagent erases the binding between the Subnet-prefixes and the mobilityagent address and sends the Subnet-prefix Binding Acknowledgement packetto the mobile router. Thereafter, the home agent stops performing theoperation of receiving the packet instead of the mobile router andforwarding the packet to the mobility agent.

[0311] (4) The mobile router sends to the mobility agent previously usedbefore the movement, the Binding Update packet including the bindingbetween the home address and the home address and indicating that theoperating mode is the active mode and that there is no need for thebuffering of packet. Receiving the Binding Update packet, the mobilityagent stores the binding between the home address and the home address,the operating mode being the active mode, and no need for the bufferingof packet, and then sends the Binding Acknowledgement packet to themobile router. Receiving the Binding Acknowledgement packet, the mobilerouter recognizes that the Binding Update packet has arrived at theprevious mobility agent and that normal processing is done. The mobilerouter further sends to the mobility agent previously used before themovement, the Subnet-prefix Binding Update packet including the bindingbetween the Subnet-prefixes of the links included in the mobile network2 and the home address and indicating that the operating mode is theactive mode and that there is no need for the buffering of packet.Receiving the Subnet-prefix Binding Update packet, the mobility agentstores the binding between the Subnet-prefixes and the home address, theoperating mode being the active mode, and no need for the buffering ofpacket, and then sends the Subnet-prefix Binding Acknowledgement packetto the mobile router. Receiving the Subnet-prefix BindingAcknowledgement packet, the mobile router recognizes that the BindingUpdate packet has arrived at the previous mobile agent and that normalprocessing is done.

[0312] (5) The mobile router sends to the correspondent host the BindingUpdate packet including the binding between the home address and thehome address. Receiving the Binding Update packet, the correspondenthost deletes the stored Binding between the home address and themobility agent address. The mobile router further sends to thecorrespondent host the Subnet-prefix Binding Update packet including thebinding between the Subnet-prefixes of the links included in the mobilenetwork 2 and the home address. Receiving the Subnet-prefix BindingUpdate packet, the correspondent host deletes the binding between theSubnet-prefixes and the mobility agent address.

[0313]FIG. 47 is an example of operation of the packet communicationsystem carried out when the operating mode transitions from the idlemode to the active mode. When during the operating mode of the idle modea node in the mobile network sends a packet to the correspondent host,the present operation example is carried out. The operation example willbe described below on the basis of FIG. 47.

[0314] (1) The mobile router sends to the mobility agent the BindingUpdate packet including the binding between the home address and the c/oaddress and indicating that the operating mode is the active mode andthat there is no need for the buffering of packet. Receiving the BindingUpdate packet, the mobility agent stores the binding between the homeaddress and the c/o address, the operating mode being the active mode,and no need for the buffering of packet, and then sends the BindingAcknowledgement packet to the mobile router. Receiving the BindingAcknowledgement packet, the mobile router recognizes that the BindingUpdate packet has arrived at the mobility agent and that normalprocessing is done. The mobile router further sends to the mobilityagent the Subnet-prefix Binding Update packet including the bindingbetween the Subnet-prefixes of the links included in the mobile network2 and the c/o address and indicating that the operating mode is theactive mode and that there is no need for the buffering of packet.Receiving the Subnet-prefix Binding Update packet, the mobility agentstores the binding between the Subnet-prefixes and the c/o address, theoperating mode being the active mode, and no need for the buffering ofpacket, and then sends the Subnet-prefix Binding Acknowledgement packetto the mobile router. Receiving the Subnet-prefix BindingAcknowledgement packet, the mobile router recognizes that theSubnet-prefix Binding Update packet has arrived at the mobility agentand that normal processing is done.

[0315] Described on the basis of FIGS. 41 to 47 above were the operationexamples in the idle mode of the packet communication system accordingto the present invention. When the mobile router moves between foreignlinks present in an area of one mobility agent, it does not have to sendthe Binding Update packet and the Subnet-prefix Binding Update packet toeither of the mobility agent, the home agent, and the correspondenthost.

[0316]FIG. 48 is an example of operation carried out when the mobilenetwork 1 moves from its home link to a foreign link and when the mobilehost moves from its home link to a foreign link in the mobile network 1.Since the operation of the mobile network 1 is the same as in theoperation examples of the mobile network 2 shown in FIGS. 33 to 47, thedescription thereof is omitted herein.

[0317] (1) After the mobile host has moved from the home link to theforeign link, it acquires a c/o address from an access router.

[0318] (2) The mobile host sends the Binding Update packet includingbinding of the home address, to-the home agent of the home link of themobile host. Receiving the Binding Update packet, the home agent of thehome link of the mobile host stores the binding between the home addressand the c/o address and sends the Binding Acknowledgement packet to themobile host. Receiving the Binding Acknowledgement packet, the mobilehost recognizes that the Binding Update packet has arrived at the homeagent of the home link of the mobile host and that normal processing isdone.

[0319] When the mobile network 1 moves between foreign links of thestationary network, the mobile network 1 operates as in the operationexamples of the mobile network 2 shown in FIGS. 38 to 41. When themobile host moves between foreign links of the mobile network 1, themobile host operates as in (1) and (2) above.

[0320]FIG. 49 is an example of operation carried out when in the activemode the correspondent host sends a packet to the mobile host present atthe foreign link of the mobile network 1. The operation example will bedescribed below on the basis of FIG. 49.

[0321] (1) The correspondent host sends the packet the destination ofwhich is the home address of the mobile host. The packet is routed tothe home link of the mobile host by the routers in the stationarynetwork.

[0322] (2) When the destination of the packet is the home address of themobile host, the home agent of the home link of the mobile host receivesthe packet instead of the mobile host, generates a tunneling packet thedestination of which is the c/o address of the mobile host of thebinding, puts the received packet into the payload of the tunnelingpacket, and sends it. The tunneling packet is routed to the home link ofthe mobile network 1 by the routers in the stationary network.

[0323] (3) When the Subnet-prefixes in the destination of the packet arethose in the binding, the home agent of the home link of the mobilenetwork .1 receives the packet instead of the mobile router, generates atunneling packet the destination of which is the mobility agent addressof the binding, puts the received tunneling packet into the payload ofthe tunneling packet, and sends it. This tunneling packet is routed tothe mobility agent by the routers in the stationary network.

[0324] (4) Receiving the tunneling packet from the home agent, themobility agent extracts the packet included therein. When theSubnet-prefixes in the destination of the extracted packet match withthose in the binding, the mobility agent puts the packet into thepayload of a tunneling packet the destination of which is the c/oaddress of the binding, and sends the tunneling packet. The tunnelingpacket is routed to the mobile router by the routers in the stationarynetwork.

[0325] (5) Receiving the tunneling packet from the mobility agent, themobile router extracts the tunneling packet from the payload. When theSubnet-prefixes in the destination match with those of the links in themobile network 1, the mobile router sends the tunneling packet into themobile network 1. The packet is routed to the mobile host by the routersin the mobile network 1. Receiving the tunneling packet directed to thec/o address, the mobile host extracts the packet from the payload toreceive the packet directed to its own home address at last.

[0326]FIG. 50 is an example of operation carried out when in the idlemode the correspondent host sends a packet to the mobile host present atthe foreign link of the mobile network 1. The operation example will bedescribed below on the basis of FIG. 50.

[0327] (1) The correspondent host sends the packet the destination ofwhich is the home address of the mobile host. The packet is routed tothe home link of the mobile host by the routers in the stationarynetwork.

[0328] (2) When the destination of the packet is the home address of themobile host, the home agent of the home link of the mobile host receivesthe packet instead of the mobile host, generates a tunneling packet thedestination of which is the c/o address of the mobile host of thebinding, puts the received packet into the payload of the tunnelingpacket, and sends it. The tunneling packet is routed to the home link ofthe mobile network 1 by the routers in the stationary network.

[0329] (3) When the Subnet-prefixes in the destination of the packet arethose in the binding, the home agent of the home link of the mobilenetwork 1 receives the packet instead of the mobile router, generates atunneling packet the destination of which is the mobility agent addressof the binding, puts the received tunneling packet into the payload ofthe tunneling packet, and sends it. The tunneling packet is routed tothe mobility agent by the routers in the stationary network.

[0330] (4) The mobility agent receives the tunneling packet from thehome agent and then extracts the tunneling packet from the payload. Whenthe destination of the extracted tunneling packet matches with theSubnet-prefixes of the binding, the mobility agent buffers the tunnelingpacket and sends the Subnet-prefix Paging Request including theSubnet-prefixes, to the access routers in the area.

[0331] (5) Receiving the Subnet-prefix Paging Request from the mobilityagent, the access routers send to their foreign links the Subnet-prefixPaging Notification in which the home address included in theSubnet-prefix Paging Request is set. The mobile router receives theSubnet-prefix Paging Notification from the access router.

[0332] (6) The mobile router judges whether the received Subnet-prefixPaging Notification includes the Subnet-prefixes of the links in thebelonging mobile network 1. Without inclusion, the mobile routerdiscards the received Subnet-prefix Paging Notification. With inclusion,the mobile router sends the Subnet-prefix Binding Update packetincluding the binding between the Subnet-prefixes and the c/o addressand indicating that the operating mode is the active mode and that thereis no need for the buffering of packet. Receiving the Subnet-prefixBinding Update packet, the mobility agent stores the binding between theSubnet-prefixes and the c/o address, the operating mode being the activemode, and no need for the buffering of packet, and then sends theSubnet-prefix Binding Acknowledgement packet to the mobile router.Receiving the Subnet-pre fix Binding Acknowledgement packet, the mobilerouter recognizes that the Subnet-prefix Binding Update packet hasarrived at the mobility agent and that normal processing is done.

[0333] (7) The mobility agent puts each buffered tunneling packet intothe payload of a tunneling packet the destination of which is the c/oaddress of the binding, and sends it. The tunneling packet is routed tothe mobile router by the routers in the stationary network.

[0334] (8) Receiving the tunneling packet from the mobility agent, themobile router extracts the tunneling packet from the payload. When theSubnet-prefixes in the destination match with those of the links in themobile network 1, the mobile router sends the tunneling packet into themobile network 1. The tunneling packet is routed to the mobile host bythe routers in the mobile network 1. Receiving the tunneling packetdirected to the c/o address, the mobile host extracts the packet fromthe payload to receive the packet directed to its own home address atlast.

[0335] Described on the basis of FIGS. 48 to 50 above were the operationexamples where the mobile host moved to the foreign link of the mobilenetwork 1 in the packet communication system of the present invention.Since the operation associated with the movement of the mobile network 1is independent of the operation associated with the movement of themobile host, when the mobile network 1 moves together with the mobilehost between foreign links of the stationary network, the mobile hostdoes not have to send the Binding Update packet to the home agent of themobile host.

[0336]FIG. 51 is an example of operation carried out when the mobilenetwork 1 moves from its home link to the foreign link and when themobile network 2 moves from its home link to a foreign link of themobile network 1. Since the operation of the mobile network 1 is thesame as in the operation examples of the mobile network 1 shown in FIGS.33 to 47, the description thereof is omitted herein.

[0337] (1) After the mobile network 2 has moved from the home link tothe foreign link of the mobile network 1, the mobile router of themobile network 2 acquires a c/o address from an access router.

[0338] (2) The mobile router of the mobile network 2 sends to the homeagent of the mobile network 2 the Binding Update packet including thebinding between the home address and the c/o address. Receiving theBinding Update packet, the home agent stores the binding between thehome address and the c/o address and sends the Binding Acknowledgementpacket to the mobile router. Receiving the Binding Acknowledgementpacket, the mobile router recognizes that the Binding Update packet hasarrived at the home agent and that normal processing is done. The mobilerouter of the mobile network 2 further sends to the home agent of thehome link of the mobile router of the mobile network 2 the Subnet-prefixBinding Update packet including the binding between the Subnet-prefixesof the links included in the mobile network 2 and the c/o address.Receiving the Subnet-prefix Binding Update packet, the home agent of thehome link of the mobile router of the mobile network 2 stores thebinding between the Subnet-prefixes and the c/o address, and sends theSubnet-prefix Binding Acknowledgement packet to the mobile router of themobile network 2. Receiving the Subnet-prefix Binding Acknowledgementpacket, the mobile router of the mobile network 2 recognizes that theSubnet-prefix Binding Update packet has arrived at the home agent of thehome link of the mobile router of the mobile network 2 and that normalprocessing is done.

[0339] When the mobile network 1 moves between foreign links of thestationary network, the mobile network 1 operates as in the operationexamples of the mobile network 2 shown in FIGS. 43 to 46. When themobile network 2 moves between foreign links of the mobile network 1,the mobile router of the mobile network 2 operates as in (1) and (2)above.

[0340]FIG. 52 is an example of operation carried out when in the activemode the correspondent host sends a packet to the stationary host of themobile network 2 present at the foreign link of the mobile network 1.The operation example will be described below on the basis of FIG. 52.

[0341] (1) The correspondent host sends the packet the destination ofwhich is the address of the stationary host. The packet is routed to thehome link of the mobile network 2 where the stationary host is present,by the routers in the stationary network.

[0342] (2) When the Subnet-prefixes in the destination of the packet arethose in the binding, the home agent of the home link of the mobilenetwork 2 receives the packet instead of the mobile router of the mobilenetwork 2, generates a tunneling packet the destination of which is thec/o address of the mobile router of the binding, puts the receivedpacket into the payload of the tunneling packet, and sends it. Thetunneling packet is routed to the home link of the mobile network 1 bythe routers in the stationary network.

[0343] (3) When the Subnet-prefixes in the destination of the tunnelingpacket are those in the binding, the home agent of the home link of themobile network 1 receives the tunneling packet instead of the mobilerouter of the mobile network 1, generates a tunneling packet thedestination of which is the mobility agent address of the binding, putsthe received tunneling packet into the payload of the tunneling packet,and sends it. The tunneling packet is routed to the mobility agent bythe routers in the stationary network.

[0344] (4) Receiving the tunneling packet from the home agent of themobile network 1, the mobility agent extracts the tunneling packetincluded in the payload. When the Subnet-prefixes in the destination ofthe extracted tunneling packet match with those in the binding, themobility agent puts the tunneling packet into the payload of a tunnelingpacket the destination of which is the c/o address of the binding, andsends it. The tunneling packet is routed to the mobile router of themobile network 1 by the routers in the stationary network.

[0345] (5) Receiving the tunneling packet from the mobility agentaddress, the mobile router of the mobile network 1 extracts thetunneling packet from the payload. When the Subnet-prefixes in thedestination match with those of the links in the mobile network 1, themobile router of the mobile network 1 sends the tunneling packet intothe mobile network 1. The packet is routed to the mobile router of themobile network 2 by the routers in the mobile network 1.

[0346] (6) Receiving the tunneling packet, the mobile router of themobile network 2 extracts the packet from the payload. When theSubnet-prefixes in the destination match with those of the links in themobile network 2, the mobile router of the mobile network 2 sends thepacket into the mobile network 2. The packet is routed to the stationaryhost by the routers in the mobile network 2. The stationary hostreceives the packet directed to its own address at last.

[0347]FIG. 53 is an example of operation carried out when in the idlemode the correspondent host sends a packet to the stationary host of themobile network 2 present at the foreign link of the mobile network 1.The operation example will be described below on the basis of FIG. 53.

[0348] (1) The correspondent host sends the packet the destination ofwhich is the address of the stationary host. The packet is routed to thehome link of the mobile network 2 at which the stationary host ispresent, by the routers in the stationary network.

[0349] (2) When the Subnet-prefixes in the destination of the packet arethose in the binding, the home agent of the home link of the mobilenetwork 2 receives the packet instead of the mobile router of the mobilenetwork 2, generates a tunneling packet the destination of which is thec/o address of the mobile router of the binding, puts the receivedpacket into the payload of the tunneling packet, and sends it. Thetunneling packet is routed to the home link of the mobile network 1 bythe routers in the stationary network.

[0350] (3) When the Subnet-prefixes in the destination of the tunnelingpacket are those in the binding, the home agent of the home link of themobile network 1 receives the tunneling packet instead of the mobilerouter of the mobile network 1, generates a tunneling packet thedestination of which is the mobility agent address of the binding, putsthe received tunneling packet into the payload of the tunneling packet,and sends it. The tunneling packet is routed to the mobility agent bythe routers in the stationary network.

[0351] (4) The mobility agent receives the tunneling packet from thehome agent and extracts the tunneling packet from the payload. When thedestination of the extracted tunneling packet matches with theSubnet-prefixes of the binding, the mobility agent buffers the tunnelingpacket and sends the Subnet-prefix Paging Request including theSubnet-prefixes, to the access routers in the area.

[0352] (5) Receiving the Subnet-prefix Paging Request from the mobilityagent, the access routers send to their foreign links the Subnet-prefixPaging Notification in which the home address included in theSubnet-prefix Paging Request is set. The mobile router receives theSubnet-prefix Paging Notification from the access router.

[0353] (6) The mobile router of the mobile network 1 judges whether thereceived Subnet-prefix Paging Notification includes the Subnet-prefixesof the links in the belonging mobile network 1. Without inclusion, themobile router discards the received Subnet-prefix Paging Notification.With inclusion, the mobile router sends the Subnet-prefix Binding Updatepacket including the binding between the Subnet-prefixes and the c/oaddress and indicating that the operating mode is the active mode andthat there is no need for the buffering of packet. Receiving theSubnet-prefix Binding Update packet, the mobility agent stores thebinding between the Subnet-prefixes and the c/o address, the operatingmode being the active mode, and no need for the buffering of packet, andthen sends the Subnet-prefix Binding Acknowledgement packet to themobile router. Receiving the Subnet-prefix Binding Acknowledgementpacket, the mobile router recognizes that the Subnet-prefix BindingUpdate packet has arrived at the mobility agent and that normalprocessing is done.

[0354] (7) The mobility agent puts each buffered tunneling packet intothe payload of a tunneling packet the destination of which is the c/oaddress of the binding. The tunneling packet is routed to the mobilerouter of the mobile network 1 by the routers in the stationary network.

[0355] (8) Receiving the tunneling packet from the mobility agent, themobile router of the mobile network 1 extracts the tunneling packet fromthe payload. When the Subnet-prefixes in the destination match withthose of the links in the mobile network 1, the mobile router of themobile network 1 sends the packet into the mobile network 1. Thetunneling packet is routed to the mobile router of the mobile network 2by the routers in the mobile network 1.

[0356] (9) Receiving the tunneling packet from the mobility agent, themobile router of the mobile network 2 extracts the packet from thepayload. When the Subnet-prefixes in the destination match with those ofthe links in the mobile network 2, the mobile router of the mobilenetwork 2 sends the packet into the mobile network 2. The packet isrouted to the stationary host by the routers in the mobile network 2.The stationary host receives the packet directed to its own address atlast.

[0357] Described on the basis of FIGS. 51 to 53 above were the operationexamples where the mobile network 2 moved to the foreign link of themobile network 1 in the packet communication system of the presentinvention. Since the operation associated with the movement of themobile network 1 is independent of the operation associated with themovement of the mobile network 2, when the mobile network 1 movestogether with the mobile network 2, the mobile router of the mobilenetwork 2 does not have to send the Binding Update packet to the homeagent of the mobile network 2.

[0358]FIG. 54 is a configuration example of a packet communicationsystem where N mobile networks 1 exist. In FIG. 54, MH represents aMobile Host, CH a Correspondent Host, each MR a Mobile Router, each HA aHome Agent, and R a Router. The configuration of each mobile network 1is the same as in FIG. 28, and has a home link and a home agent in thestationary network. The N mobile networks 1 are allowed to move to aforeign link of the stationary network or to a foreign link of anothermobile network 1.

[0359]FIG. 55 is an example of operation carried out when the N mobilenetworks 1 and the mobile host are connected like chain. Since the firstmobile network 1 stays at a foreign link of the stationary network, theoperation of the mobile router of the first mobile network 1 is the sameas in FIGS. 33 to 47. The description thereof is omitted accordingly.

[0360] (1) The mobile routers of the second to Nth mobile networks 1acquire a c/o address after movement to a foreign link of another mobilenetwork 1.

[0361] (2) The mobile routers of the second to Nth mobile networks 1send the Binding Update packet including the binding between the homeaddress and the c/o address and others, to the home agents of therespective mobile networks 1. Each home agent stores the binding andothers, and then sends the Binding Acknowledgement packet to thecorresponding mobile router. Receiving the Binding Acknowledgementpacket, each of the mobile routers determines that normal processing isdone. The mobile routers of the second to Nth mobile networks 1 furthersend to the home agents of the respective mobile networks 1, theSubnet-prefix Binding Update packet including the binding between theSubnet-prefixes of the links in each mobile network 1 and the c/oaddress and others. Each home agent stores the binding and others, andthen sends the Subnet-prefix Binding Acknowledgement packet to thecorresponding mobile router. Receiving the Subnet-prefix BindingAcknowledgement packet, each of the mobile routers determines thatnormal processing is done.

[0362] (3) When the mobile host moves to a foreign link of the Nthmobile network, it acquires a c/o address.

[0363] (4) The mobile host sends to its own home agent the BindingUpdate packet including the binding between the home address and the c/oaddress. The home agent stores the binding and sends the BindingAcknowledgement packet to the mobile host. Receiving the BindingAcknowledgement packet, the mobile host determines that normalprocessing is done.

[0364] The above operation example does not depend upon whether the Nmobile networks 1 and the mobile host are connected simultaneously orsequentially.

[0365]FIG. 56 is an example of operation carried out when during thechainlike connection of the N mobile networks 1 and the mobile host thecorrespondent host sends a packet to the mobile host.

[0366] (1) The correspondent host sends the packet the destination ofwhich is the home address of the mobile host. The packet is routed tothe home link of the mobile host by the routers in the stationarynetwork.

[0367] (2) Receiving the packet, the home agent at the home link of themobile host generates a tunneling packet the destination of which is thec/o address of the mobile host indicated by the binding, puts thereceived packet into the payload of the tunneling packet, and sends it.The tunneling packet is routed to the home link of the Nth mobilenetwork 1, which provided the c/o address for the mobile host, by therouters in the stationary network.

[0368] (3) The home agent at the home link of the Nth mobile network 1receives the tunneling packet, generates a tunneling packet thedestination of which is the c/o address of the mobile router of the Nthmobile network 1 indicated by the binding, puts the received tunnelingpacket into the payload, and sends it. The tunneling packet is routed tothe home link of the (N−1) th mobile network 1 by the routers in thestationary network.

[0369] (4) The operation described in (2) is repeated before thetunneling packet sent from the home agent at the home link of the secondmobile network is routed to the home link of the first mobile network 1.When the tunneling packet is received by the home agent of the firstmobile network 1, it includes N-multiplex tunneling packets in which thepacket first sent from the correspondent host is the innermost packetand in which the packet generated by the home agent of the second mobilenetwork 1 is the outermost packet.

[0370] (5) The home agent of the first mobile network 1 receives thetunneling packet, generates a tunneling packet the destination of whichis the mobility agent indicated by the binding, puts the receivedtunneling packet into the payload, and sends it. The multiplicity of thetunneling packet at this time is (N+1). The tunneling packet is routedto the mobility agent by the routers in the stationary network.

[0371] (6) Receiving the tunneling packet, the mobility agent extractsthe tunneling packet from the payload, generates a tunneling packet thedestination of which is the c/o address of the mobile router of thefirst mobile network indicated by the binding, and puts the extractedtunneling packet into the payload, and sends it. The multiplicity of thetunneling packet at this time is (N+1) The tunneling packet is routed tothe mobile router of the first mobile network 1 by the routers in thestationary network.

[0372] (7) Receiving the tunneling packet, the mobile router of thefirst mobile network 1 extracts the tunneling packet from the payload.When the destination of the extracted tunneling packet matches with theSubnet-prefixes of the links in the first mobile network 1, the mobilerouter of the first mobile network 1 sends the extracted tunnelingpacket. The multiplicity of the tunneling packet at this time is onesmaller than that of the tunneling packet as received, because theoutermost tunneling packet was extracted. The tunneling packet is routedto the mobile router of the second mobile network by the routers in thefirst mobile network 1.

[0373] (8) The operation described in (7) is repeated before thetunneling packet arrives at the mobile router of the Nth mobile network1.

[0374] (9) When the mobile router of the Nth mobile network receives thetunneling packet, it extracts the tunneling packet from the payload, andsends the extracted tunneling packet when the destination of theextracted tunneling packet matches with the Subnet-prefixes of the linksin the Nth mobile network 1. The tunneling packet at this time is onethe payload of which includes the packet first sent from thecorrespondent host and the destination of which is the c/o address ofthe mobile host. The tunneling packet is routed to the mobile host bythe routers of the Nth mobile network 1. Receiving the tunneling packet,the mobile host extracts the packet from the payload to receive thepacket directed to its own home address at last.

[0375]FIG. 57 is a configuration example of a packet communicationsystem where there exists a mobile network 3 having a mobility agentinside. In FIGS. 33 to 56, only the stationary network included themobility agents, but the mobile networks included no mobility agent.However, the mobile network may include a mobility agent. When amobility agent included in a certain mobile network performs theoperation of the mobility agent described in FIGS. 33 to 56, it canprovide the operating modes of the buffering of packet, the active mode,the idle mode, and so on for the mobile host and another mobile networkmoving between foreign links provided by the mobile network.

[0376]FIG. 58 is a diagram to show the operation of the mobile hostwhich is carried out after the mobile network 3 has moved to a foreignlink and when the mobile host moves to the mobile network.

[0377] (1) After the mobile host has moved from the home link to aforeign link of the mobile network 3, it acquires a c/o address and anaddress of a mobility agent from an access router.

[0378] (2) The mobile host sends to the mobility agent the BindingUpdate packet including the binding between the home address and the c/oaddress. The mobility agent stores the binding and sends the BindingAcknowledgement packet to the mobile host.

[0379] (3) The mobile host sends to its own home agent the BindingUpdate packet including the binding between the home address and themobility agent address. The home agent stores the Binding and sends theBinding Acknowledgement packet to the mobile host.

[0380]FIG. 59 is a diagram to show the operation of forwarding thepacket addressed to the mobile host, sent from the correspondent host.

[0381] (1) The correspondent host sends the packet the destination ofwhich is the home address of the mobile host. The packet is routed tothe home link of the mobile host by the routers in the stationarynetwork.

[0382] (2) When the destination of the packet is the home address of themobile host, the home agent at the home link of the mobile host receivesthe packet instead of the mobile host, generates a tunneling packet thedestination of which is the mobility agent address in the mobile network3 for the mobile host in the binding, puts the received packet into thepayload of the tunneling packet, and sends it. The tunneling packet isrouted to the home link of the mobile network 3 by the routers in thestationary network.

[0383] (3) When the Subnet-prefixes in the destination of the packet arethose in the binding, the home agent at the home link of the mobilenetwork 3 receives the packet instead of the mobile router, generates atunneling packet the destination of which is the mobility agent addressof the binding, puts the received tunneling packet into the payload ofthe tunneling packet, and sends it. This tunneling packet is routed tothe mobility agent by the routers in the stationary network.

[0384] (4) The mobility agent receives the tunneling packet from thehome agent and extracts the packet included therein. When theSubnet-prefixes in the destination of the extracted packet match withthose in the binding, the mobility agent puts the packet into thepayload of a tunneling packet the destination of which is the c/oaddress of the binding, and sends it. The tunneling packet is routed tothe mobile router by the routers in the stationary network.

[0385] (5) Receiving the tunneling packet from the mobility agent, themobile router extracts the tunneling packet from the payload and sendsthe tunneling packet into the mobile network 3 when the Subnet-prefixesin the destination match with those of the links in the mobile network3. The packet is routed to the mobility agent by the routers in themobile network 3. Receiving the tunneling packet directed to the c/oaddress, the mobility agent extracts the packet from the payload toreceive the packet directed to its own home address at last.

[0386] (6) The mobility agent receives the tunneling packet from themobile router and extracts the packet included therein. When thedestination address of the extracted packet matches with the c/o addressof the binding, the mobility agent puts the packet into the payload of atunneling packet the destination of which is the c/o address of thebinding, and sends it. The tunneling packet is routed to the mobile hostby the routers in the mobile network 3. Receiving the tunneling packetfrom the mobility agent, the mobile host extracts the packet from thepayload to receive the packet directed to its own home address at last.

[0387]FIG. 60 is an example of operation carried out when in the activemode the mobile host moves between foreign links provided by accessrouters in the area of the same mobility agent.

[0388] (1) Before moving to another foreign link, the mobile host sendsto the mobility agent the Binding Update packet including the bindingbetween the home address and the c/o address and indicating that theoperating mode is the active mode and that the buffering of packet isnecessary. Receiving the Binding Update packet, the mobility agentstores the binding between the home address and the c/o address, theoperating mode being the active mode, and the need for the buffering ofpacket, and then sends the Binding Acknowledgement packet to the mobilehost. Receiving the Binding Acknowledgement packet, the mobile hostrecognizes that the Binding Update packet has arrived at the mobilityagent and that normal processing is done. When the mobility agent isnotified of the necessity for the buffering of packet by the mobile hostand thereafter receives an applicable packet from the home agent or thecorrespondent host, the mobility agent buffers the packet directed tothe mobile host.

[0389] (2) The mobile host moves between foreign links.

[0390] (3) After the mobile host has moved to another foreign link, itacquires a c/o address and an address of a mobility agent from an accessrouter.

[0391] (4) The mobile host determines whether there is change in themobility agent address. Without change, the mobile host sends to themobility agent the Binding Update packet including the binding betweenthe home address and the c/o address and indicating that the operatingmode is the active mode and that there is no need for the buffering ofpacket. Receiving the Binding Update packet, the mobility agent storesthe binding between the home address and the c/o address, the operatingmode being the active mode, and no need for the buffering of packet, andthen sends the Binding Acknowledgement packet to the mobile host.Receiving the Binding Acknowledgement packet, the mobile host recognizesthat the Binding Update packet has arrived at the mobility agent andthat normal processing is done. When the mobility agent bears bufferedpackets, it sequentially sends the buffered packets to the mobile hostaccording to the operation similar to FIG. 10 or FIG. 11.

[0392] In the above description the mobility agents were described usingonly their fundamental form, but other forms are also conceivable.Namely, a conceivable form is such that service areas of mobility agentsoverlap with each other and access routers located in the overlappingregion can utilize a plurality of mobility agents.

[0393]FIG. 61 is a diagram to show an example of operation of accessrouters belonging to service areas of plural mobility agents. The accessrouters notifies the mobile host of availability of plural mobilityagents. Further, the access routers may notify the mobile host ofnumbers of hops to the mobility agents and selection priorities thereof.For example, as to the selection priorities, high selection prioritiesare notified of for mobility agents with low traffic applied, but lowselection priorities for mobility agents with high traffic applied.

[0394] The mobile host selects one mobility agent according to either of(1) a method of selecting a mobility agent at random, (2) a method ofpreferentially selecting a mobility agent with the smaller number ofhops to the mobility agent, (3) a method of selecting one mobility agentaccording to the selection priorities, and so on, and sends the BindingUpdate packet to the selected mobility agent.

[0395] This permits the following operation: when one mobility agentsuffers an abnormal stop due to trouble or the like, the mobile host cancontinue communications by switching to another mobility agent. It alsobecomes feasible to distribute the traffic to a plurality of mobilehosts present at a foreign link of one access router, among a pluralityof mobility agents.

[0396]FIG. 62 is a diagram to show an example of operation where themobile host uses a plurality of mobility agents.

[0397] (1) An access router located in service areas of plural mobilityagents assigns a c/o address to the mobile host and notifies the mobilehost of information on the mobility agents. The information includes thenumbers of hops to the access routers and others, in addition to theaddresses of the mobility agents. The mobile host selects two mobilityagents present on paths from the home agent to the access router.

[0398] (2) The mobile host sends to the mobility agent the BindingUpdate packet including the binding between the home address and the c/oaddress and indicating that the operating mode is the active mode andthat there is no need for the buffering of packet. Receiving the BindingUpdate packet, the mobility agent stores the binding between the homeaddress and the c/o address, the operating mode being the active mode,and no need for the buffering of packet, and then sends the BindingAcknowledgement packet to the mobile host. Receiving the BindingAcknowledgement packet, the mobile host recognizes that the BindingUpdate packet has arrived at the mobility agent and that normalprocessing is done.

[0399] (3) The mobile host sends to the other mobility agent the bindingbetween the home address and the address of the mobility agent to whichthe Binding Update packet was sent in (2).

[0400] (4) The mobile host sends to the home agent the binding betweenthe home address and the address of the mobility agent to which theBinding Update packet was sent in (3).

[0401]FIG. 63 is a diagram to show an example of operation carried outwhen the correspondent host sends a packet addressed to the mobile host.

[0402] (1) The correspondent host sends the packet the destination ofwhich is the home address of the mobile host. The packet is routed tothe home link by the routers in the network.

[0403] (2) When the destination of the packet is the home address of thebinding, the home agent of the home link receives the packet instead ofthe mobile host, generates a tunneling packet the destination of whichis the address of the first mobility agent in the binding, puts thereceived packet into the payload of the tunneling packet, and sends it.The tunneling packet is routed to the first mobility agent by therouters in the network.

[0404] (3) The first mobility agent receives the tunneling packet fromthe home agent and extracts the packet included therein. When thedestination of the extracted packet matches with the home address of thebinding, the first mobility agent puts the packet into the payload of atunneling packet the destination of which is the address of the secondmobility agent of the binding, and sends it. The tunneling packet isrouted to the second mobility agent by the routers in the network.

[0405] (4) The second mobility agent receives the tunneling packet fromthe home agent and extracts the packet included therein. When thedestination of the extracted packet matches with the home address of thebinding, the second mobility agent puts the packet into the payload of atunneling packet the destination of which is the c/o address of thebinding, and sends it. The tunneling packet is routed to the mobile hostby the routers in the network. Receiving the tunneling packet from thesecond mobility agent, the mobile host extracts the packet from thepayload to receive the packet directed to its own home address at last.

[0406] In the present invention the number of mobility agents used isnot limited to two. Namely, the number of mobility agents used may bethree or more. For example, where the distance (the number of hops) froma foreign link where the mobile host moves, to the home link is long andwhere the mobile host moves between foreign links in a wide range, itbecomes feasible to decrease the number of Binding Update transmissionsto the home agent, by connecting and using a greater number of mobilityagents.

[0407]FIG. 64 is a diagram to show an example of operation carried outwhen the mobile host moves between areas of mobility agents.

[0408] (1) Before moving to another foreign link, the mobile host sendsto the mobility agent the Binding Update packet including the bindingbetween the home address and the c/o address and indicating that theoperating mode is the active mode and that the buffering of packet isnecessary. Receiving the Binding Update packet, the mobility agentstores the binding between the home address and the c/o address, theoperating mode being the active mode, and the necessity for thebuffering of packet, and then sends the Binding Acknowledgement packetto the mobile host. Receiving the Binding Acknowledgement packet, themobile host recognizes that the Binding Update packet has arrived at themobility agent and that normal processing is done. When the mobilityagent is notified of the necessity for the buffering of packet by themobile host and thereafter receives an applicable packet from the homeagent or the correspondent host, the mobility agent buffers the packetaddressed to the mobile host.

[0409] (2) The mobile host arrives at a foreign link.

[0410] (3) An access router located in service areas of plural mobilityagents assigns a c/o address to the mobile host and notifies the mobilehost of the information on the mobility agents.

[0411] (4) The mobile host judges whether there is change in themobility agent address. With change, the mobile host sends to theprevious mobility agent the Binding Update packet including the bindingbetween the home address and the c/o address and indicating that theoperating mode is the active mode and that there is no need for thebuffering of packet. Receiving the Binding Update packet, the previousmobility agent stores the binding between the home address and the c/oaddress, the operating mode being the active mode, and no need for thebuffering of packet, and then sends the Binding Acknowledgement packetto the mobile host. Receiving the Binding Acknowledgement packet, themobile host recognizes that the Binding Update packet has arrived at theprevious mobility agent and that normal processing is done. When themobility agent bears buffered packets, it sequentially sends thebuffered packets to the mobile host according to the operation similarto FIG. 10 or FIG. 11.

[0412] (5) The mobile host sends to the mobility agent the BindingUpdate packet including the binding between the home address and the c/oaddress and indicating that the operating mode is the active mode andthat there is no need for the buffering of packet. Receiving the BindingUpdate packet, the mobility agent stores the binding between the homeaddress and the c/o address, the operating mode being the active mode,and no need for the buffering of packet, and then sends the BindingAcknowledgement packet to the mobile host. Receiving the BindingAcknowledgement packet, the mobile host recognizes that the BindingUpdate packet has arrived at the mobility agent and that normalprocessing is done.

[0413] (6) The mobile host detects that the mobility agent now under usecan be used continuously, and sends to the mobility agent the BindingUpdate packet including the binding between the home address and theaddress of the mobility agent after the change.

[0414] This can decrease the transmission frequency of Binding Updatepackets to the home agent and decrease the circuit capacity in thenetwork consumed by the Binding Update packets even if the home agent isvery far from the foreign link where the mobile host is located, i.e.,even if the number of hops is large. In the configuration using onemobility agent, the mobile host has to send the Binding Update packet tothe home agent when moving between service areas of mobility agents,whereas in the configuration using a plurality of mobility agents, themobile host is required only to send the Binding Update packet to themobility agents nearer than the home agent, which makes it feasible todecrease the transmission frequency of Binding Update packets to thehome agent.

[0415] An example of the mobile network 1 is a network in a movingobject such as a train or the like. The network in the moving object canconnect mobile hosts owned by in-vehicle users through foreign links andmove between foreign links provided by the external stationary network.On the other hand, a conceivable example of the mobile network 2 is anetwork put on a user s body (body network) carrying a plurality ofnodes connected by local wireless or wire links. The body network canmove between foreign links provided by the external stationary networkand move to a foreign link provided by the mobile network 1.

[0416] In Second Embodiment, the substantial functions of mobility agentand mobile host are the same as those of First Embodiment, and thestructures thereof is the same as those of Fist Embodiment. Therefore,detail explanation about them is omitted. It is easily understandable byreplacing home address and forwarding destination address of with Subnetprefixes 1-N that First Embodiment that these functions aresubstantially same to among them. The Second Embodiment is differentfrom the First Embodiment in use of mobile router. The structure andoperations of the mobile router will be explained below.

[0417]FIG. 65 shows a configuration of mobile router. As shown in FIG.65, mobile router MR used in the packet communication system of thepresent invention comprises a memory 300 for storing the correspondencebetween home address of the mobile router and c/o address, thecorrespondence between all Subnet-prefixes used in mobility network towhich the mobile router belongs, and c/o address of the mobile route,operation mode of the mobile router and whether or not buffering ofmobility agent using the mobile router is necessary, interface 320 forperforming reception of a packet from a link which the mobile routerconnects, and sending the packet to the link, and signal processor 330for controlling the interface 320 and the memory 300 to performprocesses of Binding Update Packet, Binding Acknowledgement Packet,Subnet-Prefixes Binding Update Packet and Subnet-prefixes BindingAcknowledgement packet, and generation/reception of packet.

[0418]FIGS. 66A, 66B and 66C are flowchart of the operations of themobile router. As shown in FIGS. 66A, 66B and 66C, the operations of themobile router are divided into operations in movement between links andoperations in reception of Subnet-prefixes Notification Packet. Beforemovement between links, the mobile router generates Binding UpdatePacket in which home address is set as the home address of the mobilerouter, c/o address is set as c/o address used in current foreign link,operation mode is set as active, buffering of packet is necessary, sendsthe Binding Update Packet to the mobility agent in an area in which themobile router is, and receives Binding Acknowledgment Packet from themobility agent. Further the mobile router generates Subnet-prefixesbinding Update Packet in which Subnet-flexes is set as allSubnet-prefixes which mobile network to which the mobile router belongs,uses, forwarding destination address is set as c/o address used in thecurrent foreign link, operation mode is set as active, and buffering ofpacket is necessary, sends the Subnet-prefixes Binding Update Packet tomobility agent in an area in which the mobile router is, and receiveSubnet-prefixes Binding Acknowledgement Packet from the mobility agent.

[0419] After movement of the mobile router to another link in themovement between links, the mobile router acquires new c/o address andaddress of mobility agent from a link to which the mobile router moved,and judges whether or not the address of the mobility agent is differentfrom address of mobility agent which is used in a link which the mobilerouter was in before the movement thereof.

[0420] 1) In case that address of mobility agent changes:

[0421] The mobile router generates Binding Update Packet in which homeaddress is set as the home address of the mobile router, c/o address isset as c/o address used in current foreign link, operation mode is setas active, buffering of packet is not necessary, sends the BindingUpdate Packet to the mobility agent in an area in which the mobilerouter is, and receives Binding Acknowledgment Packet from the mobilityagent. Further, the mobile router generates Subnet-prefixes BindingUpdate Packet in which Subnet-prefixes is set as all Subnet-prefixeswhich mobile network to which the mobile router belongs, uses,forwarding destination address is set as c/o address used in currentforeign link, operation mode is set as active, buffering of packet isnot necessary, sends the Subnet-prefixes Binding Update Packet to themobility agent in an area in which the mobile router is, and receivesSubnet-prefixes Binding Acknowledgment Packet from the mobility agent.

[0422] Next, the mobile router generates Binding Update Packet in whichhome address is set as the home address of the mobile router, forwardingdestination address is set as c/o address used in current foreign link,operation mode is set as active, buffering of packet is not necessary,sends the Binding Update Packet to the mobility agent in an area inwhich the mobile router was before the mobile router moved, and receivesBinding Acknowledgment Packet from the mobility agent. Further, themobile router generates Subnet-prefixes Binding Update Packet in whichSubnet-prefixes is set as all Subnet-prefixes which mobile network towhich the mobile router belongs, uses, forwarding destination address isset as c/o address used in current foreign link, operation mode is setas active, buffering of packet is not necessary, sends theSubnet-prefixes Binding Update Packet to the mobility agent in an areain which the mobile router was before the mobile router moved, andreceives Subnet-prefixes Binding Acknowledgment Packet from the mobilityagent.

[0423] Further the mobile router generates Binding Update Packet inwhich home address is set as the home address of the mobile router, andforwarding destination address is set as c/o address used in currentforeign link, sends the Binding Update Packet to home agent, andreceives Binding Acknowledgment Packet from the home agent. Further, themobile router generates Subnet-prefixes Binding Update Packet in whichSubnet-prefixes is set as all Subnet-prefixes which mobile network towhich the mobile router belongs, uses, sends the Subnet-prefixes BindingUpdate Packet to home agent, and receives Subnet-prefixes BindingAcknowledgment Packet from the home agent.

[0424] 2) In case that address of mobility agent does not change:

[0425] The mobile router generates Binding Update Packet in which homeaddress is set as the home address of the mobile router, forwardingdestination address is set as c/o address used in current foreign link,operation mode is set as active, buffering of packet is not necessary,sends the Binding Update Packet to the mobility agent in an area inwhich the mobile router is, and receives Binding Acknowledgment Packetfrom the mobility agent. Further, the mobile router generatesSubnet-prefixes Binding Update Packet in which Subnet-prefixes is set asall Subnet-prefixes which mobile network to which the mobile routerbelongs, uses, forwarding destination address is set as c/o address usedin current foreign link, operation mode is set as active, buffering ofpacket is not necessary, sends the Subnet-prefixes Binding Update Packetto the mobility agent in an area in which the mobile router is, andreceives Subnet-prefixes Binding Acknowledgment Packet from the mobilityagent.

[0426] Next, operations of the mobile router when the mobile routerreceives Subnet-prefixes Paging Notification Packet will be explained.

[0427] When the mobile router receives Subnet-prefixes PagingNotification Packet, the mobile router judges whether or not thereceived Subnet-prefixes Paging Notification Packet includesSubnet-prefixes which mobile network to which the mobile router belongs,uses.

[0428] 1) In the case that the received Subnet-prefixes PagingNotification Packet includes Subnet-prefixes which mobile network towhich the mobile router belongs, uses;

[0429] The mobile router generates Subnet-prefixes binding Update Packetin which Subnet-flexes is set as all Subnet-prefixes which mobilenetwork to which the mobile router belongs, uses, forwarding destinationaddress is set as c/o address used in the current foreign link,operation mode is set as active, and buffering of packet is necessary,sends the Subnet-prefixes Binding Update Packet to mobility agent in anarea in which the mobile router is, and receive Subnet-prefixes BindingAcknowledgement Packet from the mobility agent.

[0430] 2) In the case that the received Subnet-prefixes PagingNotification Packet does not includes Subnet-prefixes which mobilenetwork to which the mobile router belongs, uses;

[0431] The mobile router discards the received Subnet-prefixes PagingNotification Packet.

[0432] Further, although in the above embodiment, the mobile host ormobility agent sends binding of home address and c/o address to theprevious agent in the case that the mobile host or mobility agent movesbetween the mobility agents, the mobile router may binding of address ofnew mobility agent instead of the c/o address.

Industrial Applicability

[0433] As apparent from the above description, the present inventionprovides the following effects.

[0434] (1) Even if the mobile host frequently moves between foreignlinks, the buffering of packet at the mobility agent can prevent theloss of the packet sent from the correspondent host to the mobile host.A conceivable case where the mobile host frequently moves betweenforeign links is a situation in which the access routers in the packetcommunication system are the base stations in the mobiletelecommunications system, the mobile hosts the mobile stations, and theforeign links radio links between the base stations and the mobilestations. In this case, the movement of the mobile station between basestations, i.e., between radio links is called handover. When the presentinvention is applied to the mobile telecommunications system, it isfeasible to prevent the loss of the packet sent from the correspondenthost to the mobile station.

[0435] (2) Even if the mobile host frequently moves between foreignlinks, the mobile host is required merely to send the Binding Updatepacket to only the mobility agent. Therefore, when the mobility agent islocated nearer to the mobile host than the home agent and thecorrespondent host are, it is feasible to reduce the traffic of BindingUpdate packets appearing in the packet communication system. This effectcan also be attained in the foregoing mobile telecommunications system.

[0436] (3) When the time is long without transmission of any packet atthe mobile host, the idle mode is used whereby it is feasible to reducethe traffic of Binding Update packets appearing in the packetcommunication system. Further, since the transmission frequency ofBinding Update packets from the mobile host can be reduced, theinvention also provides the effect of decreasing the power consumptionof the battery at the mobile host. This effect is also achieved in theforegoing mobile telecommunications system.

[0437] (4) The invention presents the effect that the correspondent hostcan send the packet whose destination is the stationary host or themobile host located at the mobile network. This effect is not enjoyedonly when the packet has the destination of a node located at a networkconnected to the stationary network, but is also enjoyed similarly whenthe packet has the destination of a stationary host or a mobile hostlocated at a mobile network connected to another mobile network.

1. A mobility agent for forwarding a received packet to a mobile host onthe basis of the destination address included in the received packet,comprising; memory means for storing data included in a signal sent fromthe mobile host, the data representing the correspondence between thehome address and the forwarding destination address, operation mode, andwhether or hot buffering of a packet is necessary every the mobile host;and sending means for sending a reception acknowledgement signal to themobile host which sent the signal, when the memory means has stored thedata.
 2. The mobility agent according to claim 1, further comprisingsending/receiving control means for judging information regardingcorrespondence between home address of the mobile host corresponding todestination address and forwarding destination address included in thereceived packet, operation mode of the mobility agent, and necessity ofbuffering of packet, and controlling sending/receiving of the receivedpacket on the basis of the information.
 3. The mobility agent accordingto claim 2, wherein the sending/receiving controlling means judges anoperation status of mobile host corresponding to destination address ofthe received packet and a status of the necessity of the buffering ofpacket, and sending the received packet to forwarding destinationaddress of the mobile host, when the operation mode of the correspondentmobile host is active and buffering of packet therein is not necessary.4. The mobility agent according to claim 2 or 3, wherein thesending/receiving controlling means judges an operation status of mobilehost corresponding to destination address of the received packet and astatus of the necessity of the buffering of packet, and causes thememory means store the receive packet, when the operation mode of thecorrespondent mobile host is active and buffering of packet therein isnecessary.
 5. The mobility agent according to claim 2, 3 or 3, whereinthe sending/receiving controlling means judges an operation status ofmobile host corresponding to destination address of the received packetand a status of the necessity of the buffering of packet, and causes thememory means store the receive packet as well as notifies the arrival ofthe packet to the mobile host, when the operation mode of thecorrespondent mobile host is idle and buffering of packet therein isnecessary.
 6. A method of controlling a mobility agent forwarding thereceived packet to a mobile host on the basis of destination address inthe packet, comprising; a receiving step of receiving data included in asignal sent from the mobile host, the data representing thecorrespondence between the home address and the forwarding destinationaddress, operation mode, and whether or not buffering of a packet isnecessary a storing step of storing the data received in the receivingstep; and a sending step of sending a reception acknowledgement signalto the mobile host which sent the data when the storing in the storingstep is completed.
 7. The method of controlling the mobility agentaccording to claim 6, further comprising a judging step of judginginformation regarding correspondence between home address of the mobilehost corresponding to destination address and forwarding destinationaddress included in the received packet, operation mode of the mobilityagent, and necessity of buffering of packet.
 8. The method ofcontrolling the mobility agent according to claim 7, further comprisinga sending step of the received packet to the mobile host when in thejudging step, an operation status of mobile host corresponding todestination address of the received packet and a status of the necessityof the buffering of packet is judged, and when it is judged that theoperation mode of the correspondent mobile host is active and bufferingof packet therein is not necessary.
 9. The method of controlling themobility agent according to claim 7 or 8, further comprising a step ofcausing the memory means store the received packet, when in the judgingstep, an operation status of mobile host corresponding to destinationaddress of the received packet and a status of the necessity of thebuffering of packet is judged, and when it is judged that the operationmode of the correspondent mobile host is active and buffering of packettherein is not necessary.
 10. The method of controlling the mobilityagent according to claim
 7. 8 or 9, further comprising a step of storingthe received packet, when a sending step of the received packet to themobile host when in the judging step, an operation status of mobile hostcorresponding to destination address of the received packet and a statusof the necessity of the buffering of packet is judged, and when it isjudged that the operation mode of the correspondent mobile host is idleand buffering of packet therein is not necessary, and a notificationstep of notifying the arrival of the packet to the mobile host.
 11. Acompute program executable by a compute, wherein the computer program iscarried out by a method according to any one of claims 6-10.
 12. Amobile host which performs the packet communication between the mobilehost and the correspondence host, comprising; a first sending means forforwarding of data representing the correspondence between home addressof the mobile host and forwarding destination address, the operationmode, either one of active mode or idle mode of the mobile host, anddata requesting whether or not buffering of the packet is not necessaryin a packet to be received, to the mobility agent; and receiving meansfor receiving a reception acknowledgement signal sent by the sendingmeans.
 13. The mobile host according to claim 12, further comprisingsecond sending means for sending correspondence between home address ofthe mobile host and address of the mobility agent which uses the mobilehost, to a home agent which the mobile host uses.
 14. The mobile hostaccording to claim 12, further comprising operation mode changing meansfor changing the operation mode of the mobile host to a active mode,when in idle mode operation of the mobile host, the mobile host receivea paging signal including home address of the mobile host, and thirdsending means for sending a signal representing that the operation modeof the mobile host changed to active mode, to the mobility agent sendinga paging notification signal.
 15. The mobile host according to claim 12,further comprising sending/receiving control means, in the case that themobile host moves between foreign links in an area of the predeterminedmobility agent, for notifying a signal representing correspondencebetween home address and c/o address of the mobile host and that theoperation mode of the mobile host is active and requesting buffering ofa received packet to a predetermined mobility agent before the mobilehost moves to a foreign link, and notifying correspondence between homeaddress of the mobile host and c/o address utilized in the foreign linkto which the mobile host moves, in active mode of the mobile host, andno necessary of buffering of the packet, to the predetermined mobilityagent after the mobile host has moved to the foreign link.
 16. Themobile host according to claim 12, further comprising, in the case thatthe mobile host moves from a first foreign link in an area of a firstmobility agent to a second foreign link in an area of a second mobilityagent, sending/reception control means for notifying a signalrepresenting correspondence between home address of the mobility hostand c/o address, and that operation mode of the mobile host is active,and requesting no necessity of buffering of packet, to the firstmobility agent, before the mobile host moves from the first foreignlink, and for notifying correspondence between home address of themobile host and c/o address which is used in the second foreign link towhich the mobile moves, that operation mode of the mobile host isactive, and that buffering of the packet is not necessary, to the firstmobility agent, receiving a packet buffered in and sent from the firstmobility in response to the notification, and further sending a signalincluding correspondence between the home address and address of thesecond mobility agent to the home agent after the mobile host has movedto the second foreign link.
 17. A method of controlling a mobile hostwhich performs packet communication to correspondent host, comprising; asending step of sending data representing operation mode of the mobilehost, either of active mode or a idle mode, and data instructing whetheror not buffering of packet is necessary, to a mobility agent; and areceiving step of receiving a reception acknowledgement date of the datasent in the sending step.
 18. The method of controlling a mobile host,further comprising a second sending step of sending data representingcorrespondence between the home address of the mobile host and addressof the mobility agent which connects to the mobile host, to home agentwhich connects to the mobile host.
 19. The method of controlling amobile host according to claim 17, further comprising operation modechanging step of changing the operation mode of the mobile host to aactive mode, when in idle mode operation of the mobile host, the mobilehost receive a paging signal including home address of the mobile host,and a third sending step of sending a signal representing that theoperation mode of the mobile host changed to active mode, to themobility agent sending a paging notification signal.
 20. The method ofcontrolling a mobile host according to claim 17, further comprising, inthe case that the mobile host moves between foreign links in an area ofthe predetermined mobility agent, a notification step of notifying asignal representing correspondence between home address and c/o addressof the mobile host and that the operation mode of the mobile host isactive and requesting buffering of a received packet to a predeterminedmobility agent before the mobile host moves to a foreign link, and asecond notification step of notifying correspondence between homeaddress of the mobile host and c/o address utilized in a foreign link towhich the mobile host moves, in active mode of the mobile host, and nonecessary of buffering of the packet, to the predetermined mobilityagent, after the mobile host has moved to the foreign link.
 21. Themethod of controlling a mobile host, according to claim 17, furthercomprising, in the case that the mobile host moves from a first foreignlink in an area of a first mobility agent to a second foreign link in anarea of a second mobility agent, a notification step of notifying asignal representing correspondence between home address of the mobilityhost and c/o address, and that operation mode of the mobile host isactive, and requesting no necessity of buffering of packet, to the firstmobility agent, before the mobile host moves from the first foreignlink, a second notification step of notifying correspondence betweenhome address of the mobile host and c/o address which is used in thesecond foreign link to which the mobile moves, that operation mode ofthe mobile host is active, and that buffering of the packet is notnecessary, to the first mobility agent, after the mobile host has movedto the second foreign link, a receiving step of receiving a packetbuffered in and sent from the first mobility in response to thenotification, and a sending step of sending a signal includingcorrespondence between the home address and address of the secondmobility agent to the home agent after the mobile host has moved to thesecond foreign link.
 22. A compute program executable by a compute,wherein the computer program is carried out by a method according to anyone of claims 17-21.
 23. A mobile router for forwarding a packet ofwhich destination address is not address of the mobile router, toanother node, between a mobile network and a stationary network, orbetween stationary networks, comprising; a first sending means forforwarding of data representing the operation mode, either one of activemode or idle mode of the mobile router, and data instructing whether ornot buffering of packet is necessity in a packet to be received, to amobility agent; and receiving means for receiving a receptionacknowledgement signal sent by the sending means.
 24. The mobile routeraccording to claim 23, further comprising second sending means forsending correspondence between home address of the mobile router andaddress of the mobility agent which uses the mobile router, andcorrespondence between all Sub-prefixes which mobile network to whichthe mobile router belongs and c/o address of the mobile router to a homeagent which the mobile router uses.
 25. The mobile router according toclaim 23, further comprising sending/reception control means for, whenthe mobile router receives a paging notification signal including a homeaddress of the mobile router or a Subnet-prefixes which a mobile networkto which the mobile router belongs to, during in idle mode of the mobilerouter, judging whether or not a received subnet-prefixes pagingnotification packet includes the Subnet-prefixes which a mobile networkto which the mobile router belongs to, when it is judged that thereceived subnet-prefixes paging notification packet includes theSubnet-prefixes which a mobile network to which the mobile routerbelongs to, generating a subnet-prefixes binding update packet in whichsubnet-prefixes is set as all subnet-prefixes which mobile network towhich the mobile router belongs to, uses, forwarding destination addressis set as c/o address whish the mobile router uses in current foreignlink, the operation mode of the mobile router is active, and bufferingof packet is not necessary, and receiving a subnet-prefixes bindingacknowledgment packet from the mobility agent, and when it is judgedthat the received subnet-prefixes paging notification packet does notincludes the Subnet-prefixes which a mobile network to which the mobilerouter belongs to, discarding the received subnet-prefixes pagingnotification packet.
 26. The mobile router according to claim 23,further comprising sending/receiving control means, in the case that themobile router moves between foreign links in an area of a predeterminedmobility agent, for notifying correspondence between home address of themobile router and c/o address, correspondence between allsubnet-prefixes which a mobile network to which the mobile routerbelongs and c/o address of the mobile router, that the operation mode ofthe mobile host is active and request of buffering of a received packet,to a predetermined mobility agent before the mobile host moves to aforeign link, before the mobile router moves to a foreign link, and fornotifying correspondence between home address of the mobile router andc/o address utilized in the foreign link to which the mobile routermoves, in active mode of the mobile router, and no necessary ofbuffering of the packet, to the predetermined mobility agent after themobile router has moved to the foreign link.
 27. The mobile routeraccording to claim 23, further comprising, sending/reception controlmeans, in the case that the mobile router moves from a first foreignlink in an area of a first mobility agent to a second foreign link in anarea of a second mobility agent, for notifying a signal representingcorrespondence between home address of the mobility router and c/oaddress which the mobile router uses in the first foreign network,correspondence between all subnet-prefixes of mobile network to whichthe mobile router belongs and c/o address which the mobile router usesin the first foreign link, and that operation mode of the mobile host isactive, and requesting necessity of buffering of packet, to the firstmobility agent, before the mobile router moves from the first foreignlink, and for notifying correspondence between home address of themobile router and c/o address which is used in the second foreign link,correspondence between all subnet fixes of mobile network to which themobile router belongs and c/o address which the mobile router uses inthe second foreign link, that operation mode of the mobile router isactive, and that buffering of the packet is not necessary, to the firstmobility agent, receiving a packet buffered in and sent from the firstmobility agent in response to the notification, and further sending asignal including correspondence between the home address of the mobilerouter and address of the second mobility agent, and correspondencebetween all subnet-fixes and address of the second mobility agent, tothe home agent after the mobile host has moved to the second foreignlink.
 28. A method of controlling a mobile router for forwarding apacket of which destination address is not address of the mobile router,to another node, between a mobile network and a stationary network, orbetween stationary networks, comprising; a sending step of sending datarepresenting the operation mode, either one of active mode or idle modeof the mobile router, and data instructing whether or not buffering ofpacket is necessity in a packet to be received, to a mobility agent; anda reception step of receiving a reception acknowledgement signal sent bythe sending means.
 29. The method of controlling a mobile routeraccording to claim 28, further comprising a second sending step ofsending correspondence between home address of the mobile router andaddress of the mobility agent which uses the mobile router, andcorrespondence between all Sub-prefixes which mobile network to whichthe mobile router belongs and c/o address of the mobile router to a homeagent which the mobile router uses.
 30. The method of controlling amobile router according to claim 28, further comprising asending/reception control step of, when the mobile router receives apaging notification signal including a home address of the mobile routeror a Subnet-prefixes which a mobile network to which the mobile routerbelongs to, during in idle mode of the mobile router, judging whether ornot a received subnet-prefixes paging notification packet includes theSubnet-prefixes which a mobile network to which the mobile routerbelongs to, when it is judged that the received subnet-prefixes pagingnotification packet includes the Subnet-prefixes which a mobile networkto which the mobile router belongs to, generating a subnet-prefixesbinding update packet in which subnet-prefixes is set as allsubnet-prefixes which mobile network to which the mobile router belongsto, uses, forwarding destination address is set as c/o address whish themobile router uses in current foreign link, the operation mode of themobile router is active, and buffering of packet is not necessary, andreceiving a subnet-prefixes binding acknowledgment packet from themobility agent, and when it is judged that the received subnet-prefixespaging notification packet does not includes the Subnet-prefixes which amobile network to which the mobile router belongs to, discarding thereceived subnet-prefixes paging notification packet.
 31. The method ofcontrolling a mobile router according to claim 28, further comprising asending/receiving control step of, in the case that the mobile routermoves between foreign links in an area of a predetermined mobilityagent, notifying correspondence between home address of the mobilerouter and c/o address, correspondence between all subnet-prefixes whicha mobile network to which the mobile router belongs and c/o address ofthe mobile router, that the operation mode of the mobile host is activeand request of buffering of a received packet, to a predeterminedmobility agent before the mobile host moves to a foreign link, beforethe mobile router moves to a foreign link, and notifying correspondencebetween home address of the mobile router and c/o address utilized inthe foreign link to which the mobile router moves, in active mode of themobile router, and no necessary of buffering of the packet, to thepredetermined mobility agent after the mobile router has moved to theforeign link.
 32. The method of controlling a mobile router according toclaim 28, further comprising, a sending/reception control step of, inthe case that the mobile router moves from a first foreign link in anarea of a first mobility agent to a second foreign link in an area of asecond mobility agent, notifying a signal representing correspondencebetween home address of the mobility router and c/o address which themobile router uses in the first foreign network, correspondence betweenall subnet-prefixes of mobile network to which the mobile router belongsand c/o address which the mobile router uses in the first foreign link,and that operation mode of the mobile host is active, and requestingnecessity of buffering of packet, to the first mobility agent, beforethe mobile router moves from the first foreign link, and notifyingcorrespondence between home address of the mobile router and c/o addresswhich is used in the second foreign link, correspondence between allsubnet fixes of mobile network to which the mobile router belongs andc/o address which the mobile router uses in the second foreign link,that operation mode of the mobile router is active, and that bufferingof the packet is not necessary, to the first mobility agent, receiving apacket buffered in and sent from the first mobility agent in response tothe notification, and further sending a signal including correspondencebetween the home address of the mobile router and address of the secondmobility agent, and correspondence between all subnet-fixes and addressof the second mobility agent, to the home agent after the mobile hosthas moved to the second foreign link.
 33. A compute program executableby a compute, wherein the computer program is carried out by a methodaccording to any one of claims 28-32.
 34. A packet communication systemcomprising a home agent for providing a home link for a mobile host, aplurality of access routers for providing foreign links for the mobilehost, and a mobility agent including a plurality of access routers in anarea thereof, in which a home address is used when the mobile host ispresent at the home link and in which the home address and a c/o addressare used when the mobile host is present at a foreign link, wherein themobile host comprises: first notifying means for notifying the mobilityagent of a correspondence between the home address and the c/o address,an operating mode indicating either an active mode or an idle mode, andwhether or not buffering of a packet is necessary; and second notifyingmeans for notifying the home agent of a correspondence between the homeaddress and an address of the mobility agent, wherein the home agentcomprises: first forwarding means for forwarding a packet directed tothe home address, received from a correspondent host, to the address ofthe mobility agent notified of by the mobile host, wherein thecorrespondent host comprises sending means for sending a packet directedto the home address, to the address of the mobility agent notified of bythe mobile host, wherein the mobility agent comprises: second forwardingmeans for forwarding a packet received from the home agent or thecorrespondent host, to the mobile host; and buffering means forbuffering a packet; and third notifying means for notifying the mobilehost of arrival of a packet, and wherein the mobility agent isconfigured so that in the active mode and without necessity forbuffering of a packet, the mobility agent forwards a packet receivedfrom the home agent or the correspondent host, to the mobile host, sothat in the active mode and with necessity for buffering of a packet,the mobility agent buffers a packet, and so that in the idle mode themobility agent buffers a packet and notifies the mobile host of arrivalof the packet.
 35. The packet communication system according to claim34, comprising a plurality of mobility agents.
 36. The packetcommunication system according to claim 34 or claim 35, wherein in theactive mode, where the mobile host moves between foreign links in thearea of the mobility agent, the mobile host notifies the mobility agentof the correspondence between the home address and the c/o address, theoperating mode indicating the active mode, and the necessity forbuffering of a packet, before moving between the foreign links, and themobile host notifies the mobility agent of a correspondence between thehome address and a c/o address used at the destination foreign link, theoperating mode indicating the active mode, and no necessity forbuffering of a packet, after having moved between the foreign links, andin the case that the mobile host moves between foreign links in an areaof the mobility agent, the mobile host notifies correspondence betweenhome address and c/o address of the mobile host the operation mode inactive and necessary of buffering of packet to the mobility agent beforethe mobile host moves to the foreign link, and further notifiescorrespondence between home address of the mobile host and c/o addressutilized in the foreign link to which the mobile host moves, in activemode of the mobile host, and no necessary of buffering of the packet, tothe mobility agent after the mobile host has moved to the foreign link.37. The packet communication system according to claim 34 or claim 35,wherein in the idle mode, where the mobile host moves between foreignlinks in the area of the mobility agent, the mobile host notifiesneither of the mobility agent, the home agent, and the correspondenthost of anything.
 38. The packet communication system according to claim35, wherein in the active mode, where the mobile host moves from aforeign link in an area of a certain mobility agent to a foreign link inan area of another mobility agent different therefrom, the mobile hostnotifies the mobility agent of the correspondence between the homeaddress and the c/o address, the operating mode indicating the activemode, and the necessity for buffering of a packet, before moving betweenthe foreign links, the mobile host notifies the mobility agent of acorrespondence between the home address and a c/o address used at thedestination foreign link, the operating mode indicating the active mode,and no necessity for buffering of a packet and also notifies the homeagent and the correspondent host of a correspondence between the homeaddress and an address of the mobility agent after having moved betweenthe foreign links, and the previous mobility agent sends a packetbuffered therein and corresponding to the mobile host to the mobilehost, and further sends binding of the home address and the address ofthe another mobility to the home agent.
 39. The packet communicationsystem according to claim 35, wherein in the idle mode, where the mobilehost moves from a foreign link in an area of a certain mobility agent toa foreign link of another mobility agent different therefrom, the mobilehost notifies the mobility agent of a correspondence between the homeaddress and a c/o address used at the destination foreign link, theoperating mode indicating the idle mode, and the necessity for bufferingof a packet and also notifies the home agent and the correspondent hostof a correspondence between the home address and an address of themobility agent, after having moved between the foreign links.
 40. Thepacket communication system according to any one of claim 34 to claim39, wherein the home agent and access routers are base stations, thehome link and foreign links are radio communication links, and themobile host is a mobile station.
 41. A packet communication systemcomprising a stationary network and a mobile network, wherein saidstationary network comprises a home agent adapted to said mobilenetwork, a mobility agent, a correspondent host, and an access router,wherein said mobile network comprises at least one mobile router and aplurality of access routers, and wherein said mobile network movesbetween foreign links provided by said stationary network or anothermobile network.
 42. A packet communication system comprising astationary network and a mobile network, wherein said stationary networkcomprises a home agent adapted to said mobile network, a mobility agent,a correspondent host, and an access router, wherein said mobile networkcomprises at least one mobile router and a plurality of stationaryhosts, and wherein said mobile network moves between foreign linksprovided by said stationary network or another mobile network.
 43. Thepacket communication system according to claim 41 or claim 42, whereinsaid mobile router comprises: first notifying means for notifying themobility agent of a correspondence between a home address and a c/oaddress, an operating mode indicating either an active mode or an idlemode, and whether or not buffering of a packet is necessary; secondnotifying means for notifying the home agent of a correspondence betweenthe home address and an address of the mobility agent; and Subnet-prefixnotifying means for notifying said mobility agent and said home agent ofa Subnet-prefix for identifying a link included in the mobile network.44. The packet communication system according to either of claim 42 toclaim 44, wherein said mobile network comprises at least one mobilityagent.
 45. The packet communication system according to either of claim41 to claim 44, wherein, when an access router exists in an area whereservice areas of a plurality of mobility agents overlap with each other,said access router is free to select either one of said plurality ofmobility agents.